|Celebes| Sula |Sanghir| Range and
| | Is. | Is. | Remarks
--------------------------------+-------+-------+-------+-------------
TURDIDAE. | | | |
1. Geocichla erythronota | X | | |
2. Monticola solitaria | X | | X |Phil., China,
| | | | Japan
| | | |
SYLVIIDAE. | | | |
3. Cisticola cursitans | X | | |Assam
4 ,, grayi | X | | |
5. Acrocephalus orientalis | X | | |China, Japan
*6. ,, insularis | -- | -- | X |Moluccas
| | |(Salv.)|
7. Pratincola caprata | X | | |Asia, Java,
| | | | Timor
*8. Gerygone flaveola (Cab.) | X | | |(Near G.
|(Meyer)| | |_sulphurea_,
| | | |Timor)
| | | |
TIMALIIDAE. | | | |
9. Trichostoma celebense | X | | |
| | | |
PYCNONOTIDAE. | | | |
*10. Criniger longirostris | | | |
(Wall.) | | X | |Oriental
| | | | genus (near
| | | | Bouru sp.)
11. ,, aureus (Wald.) | X | | |
| | | |
ORIOLIDAE. | | | |
12. Oriolus celebensis | X | | |(Var of O.
| | | | _coronatus_,
| | | | Java)
13. ,, formosus (Cab.) | -- | -- | X |(Var. of
| | |(Brugg.) Philipp.
| | | | sp.)
14. ,, frontalis (Wall.) | -- | X | |
| | | |
CAMPEPHAGIDAE. | | | |
15. Graucalus atriceps | X | | |Ceram, Flores
16. ,, leucopygius | X | | |
17. ,, temminckii | X | X | |
18. Campephaga morio | X | | |
*19. ,, melanotis | -- | X | |Moluccas
*20. ,, salvadorii | |(Wall.)| |
(Sharpe) | -- | -- | X |
21. Lalage leucopygialis | X | | |
*22. ,, dominica | X | -- | -- |Java
|(Meyer)| | |
23. Artamides bicolor | X | | |
*24. ,, schistaceus | | | |
(Sharpe) | -- | X | |
| | | |
DICRURIDAE. | | | |
25. Dicrurus leucops | X | | |
*26. ,, axillaris (Salv.) | -- | -- | X |
*27. ,, pectoralis (Wall.) | | X | |
{467}
| | | |
MUSCICAPIDAE. | | | |
28. Cyornis rufigula | X | | |
29. ,, banyumas | X | | |Java and Borneo
30. Myialestes helianthea | X | | |(Indian ally)
31. Hypothymis puella | X | X | |
32. ,, menadensis? | X | | |
*33. Monarcha commutata | | | |
(Brugg.) | X | | |
*34. ,, cinerascens | -- | X | |Moluccas
| |(Wall.)| |
PACHYCEPHALIDAE. | | | |
35. Hylocharis sulfuriventra | X | | |
*36. Pachycephala lineolata | | | |
(Wall.) | -- | X | -- |Bouru
*37. Pachycephala rufescens | | | |
(Wall.) | -- | X | -- |Bouru
*38. Pachycephala clio (Wall.) | -- | X | -- |Bouru
| | | |
LANIIDAE. | | | |
*39. Lanius magnirostris (Meyer)| X | -- | -- |Java
| | | |
CORVIDAE. | | | |
40. Corvus enca | X | X var.| |Java
*41. ,, annectens (Brugg.) | X | | |
42. ,,(Gazzola) typica | X | | |
43. Streptocitta caledonica | X | | |
44. ,, torquata | X | | |
*45(Charitornis)albertiae(Schl.)| -- | X | |
| | | |
MELIPHAGIDAE. | | | |
46. Myzomela chloroptera | X | | |(Nearest _M.
| | | |sanguinolenta_
| | | |of Australia)
NECTARINIIDAE. | | | |
47. Anthreptes celebensis | | | |
(Shelley) | X | X | X |Siam, Malaya
48. Chalcostethia porphyolaema | X | | |
*49. ,, auriceps | -- | X | -- |Ternate
| |(Wall.)| |
*50. ,, sangirensis | -- | -- | X |
(Meyer) | | | |
51. Cyrtostomus frenatus | X | X | -- |Moluccas and N.
| | | | Guinea
52. Nectarophila grayi | X | | |
53. Aethopyga flavostriata | X | | |(An Oriental
| | | | genus)
*54. ,, beccarii (Salv.) | X | | |
*55. ,, duyvenbodei (Schl.)| -- | -- | X |
| | | |
DICAEIDAE. | | | |
56. Zosterops intermedia | X | | |Lombock
57. ,, atrifrons | X | | |
58. Dicaeum celebicum | X | X | |
*59. ,, sanghirense (Salv.) | -- | -- | X |
*60. ,, nehrkorni (Blas.) | X | | |
61. Pachyglossa aureolimbata | X | -- | X |
| | | |
HIRUNDINIDAE. | | | |
62. Hirundo gutturalis | X | | X |Indian region
63. ,, javanica | X | X | |Indo-Malaya
| | | |
PLOCEIDAE. | | | |
64. Munia oryzivora | X | | |Java
65. ,, nisoria | X | | |Java
66. ,, molucca | X | | |Moluccas
{468}
67. ,, brunneiceps | X | | |(Near _M.
| | | |rubronigra_,
| | | |India)
*68. ,, jagori | X | | |Philippines
|(Meyer)| | |
STURNIDAE. | | | |
69. Basilornis celebensis | X | | |
70. Acridotheres cinereus | X | | |
71. Sturnia pyrrhogenys | X | | |Malaya
72. Calornis neglecta | X | X | X var.|
*73. ,, metallica | X | X | |Moluccas
|(Brugg.)(Wall.)| |
74. Enodes crythrophrys | X | | |
75. Scissirostrum pagei | X | | |
| | | |
ARTAMIDAE. | | | |
76. Artamus monachus | X | X | |
77. ,, leucorhynchus | X | | |Malay Archipel.
| | | |
MOTACILLIDAE. | | | |
78. Corydalla gustavi | X | | |
79. Budytes viridis | X | | |Java, Moluccas
*80. Calobates melanope | | | |
(= Motac. sulfurea, Brugg.) | X | | |China, Phillipp.
| | | |
PITTIDAE. | | | |
81. Pitta forsteni | X | | |
*82. ,, sanghirana (Schl.) | | | X |
83. ,, celebensis | X | | |
*84. ,, palliceps (Brugg.) | | | X |
*85. ,, coeruleitorques (Salv.) | | X |
*86. ,, irena (= crassirostris) | X | |Timor, Ternate?
| |(Wall.)| |
PICIDAE. | | | |
87. Alophonerpes fulvus | X | | |
*88. ,, wallacei | | | |
89. Yungipicus temminckii | X | | |
| | | |
CUCULIDAE. | | | |
90. Rhamphococcyx calorhynchus | X | | |
91. Pyrrhocentor celebensis | X | | |
92. Centropus affinis | X | | |Java
93. ,, javanensis | X | | |Java, Borneo
94. Cuculus canorus | X | | |
95. Cacomantes lanceolatus | X | | |Java
96. ,, sepulchralis | X | | |
97. Hierococcyx crassirostris | X | | |
98. Eudynamis melanorhyncha | X | | |
*99. ,, facialis (Wall.) | | X | |
*100. ,, orientalis | | | X |Moluccas?
| | |(Brugg.)
101. Scythrops novaehollandiae | X | | |Moluccas, &c.
| | | |
CORACIIDAE. | | | |
102. Coracias temminckii | X | | |
103. Eurystomus orientalis | X | X | X |Asia
| | | |
MEROPIDAE. | | | |
104. Meropogon forsteni | X | | |
105. Merops philippinus | X | | |Oriental region
106. ,, ornatus | X | X | |Java, Australia
| | | |
ALCEDINIDAE. | | | |
107. Alcedo moluccensis | X | | X |Moluccas
108. ,, asiatica | X | | |Indo-Malaya
{469}
109. Pelargopsis melanorhyncha | X | X | |
*110. Ceyx wallacei (Sharpe) | | X | |(Allied to Mol.
| | | | sp.)
111. Ceycopsis fallax | X | | |
112. Halcyon chloris | X | X | X |All Archipel.
113. ,, sancta | X | X | |All Archipel.
114. ,, forsteni | X | | |
115. ,, rufa | X | X | |
116. Monachalcyon princeps | X | | |
*117. ,, cyanocephala (Brugg.) | X | | |
118. Cittura cyanotis | X | | |
*119. ,, sanghirensis (Schl.)| | | X |
| | | |
BUCEROTIDAE. | | | |
120. Hydrocissa exarata | X | | |
121. Cranorhinus cassidix | X | | |
| | | |
CAPRIMULGIDAE. | | | |
122. Caprimulgus affinis | X | | |
123. ,, sp. | X | | |
124. Lyncornis macropterus. | X | | |
| | | |
CYPSELIDAE. | | | |
125. Dendrochelidon wallacei | X | X | |
126. Collocalia esculenta | X | | |Mol. to Arn Is.
127. ,, fuciphaga | X | | |India, Java
128. Chaetura gigantea | X | | |India, Java
| | | |
PSITTACI. | | | |
129. Cacatua sulphurea | X | | |Lombock, Flores
130. Prioniturus platurus | X | | |
131. ,, flavicans | X | | |
*132. Platycercus dorsalis, var.| | X | |N. Guinea?
| |(Wall.)| |
133. Tanygnathus mulleri | X | X | |
*134. ,, megalorhynchus | X | | X |Moluccas. An
| | | |island near
| | | |Menado (Meyer)
*135. ,, luzoniensis | | | X |
| | |(Brugg.)
136. Loriculus stigmatus | X | | |
*137. ,, quadricolor (Wald.)| X | | |Togian Is., Gulf
| | | |of Tomini
138. ,, sclateri | ? | X | |
139. ,, exilis | X | | |
*140. ,, catamene (Schl.) | | | X |
141. Trichoglossus ornatus | X | | |
*142. ,, flavoviridis (Wall.)| | X | |
143. ,, meyeri | X | | |
*144. Eos histrio = E. coccinea | | | X |
| | | |
COLUMBAE. | | | |
145. Treron vernans | X | | |Malacca, Java,
| | | |Philipp.
146. ,, griseicauda | X | X | X var.|
| | |Sanghir-
| | | ensis |
147. Ptilopus formosus | X | | |
148. ,, melanocephalus | X | X | X var.|Java, Lombock
| | |Xantho-|
| | | rrhoa,|
| | |Salv. |
149. ,, gularis | X | | |
*150. ,, fischeri (Brugg.)| X | | |
151. Carpophaga paulina | X | X | |
{470}
*152. ,, pulchella | X | | |Togian Is.
(Wald.) | | | |(_Ann. and
| | | |Mag. Nat. Hst._,
| | | |1874.)
153. ,, concinna | | | X |Ke Goram
| | |(Salv.)|
154. ,, rosacea | X | | |Gilolo, Timor
*155. ,, paecilorrhoa (Brugg)| X | | |
156. ,, luctuosa | X | X | |
*157. ,, bicolor | X | | X |New Guin.,
|(Meyer)| | |Moluccas
158. ,, radiata | X | | X |
159. ,, forsteni | X | | |
160. Macropygia albicapilla | X | X | |
161. ,, macassariensis | X | | |
*162. ,, sanghirensis (Salv.) | | | X |
163. Turacoena menadensis | X | X | |
*164. Reinwardtaenas reinwardti |X Meyer| | |Moluccas & New
| | | |Guin.
165. Turtur tigrina | X | | |Malaya, Moluccas
166. Chalcophaps stephani | X | | |New Guinea
167. ,, indica | X | X var.| X |India and
| | | |Archipel.
168. Phlogaenas tristigmata | X | | |
169. Geopelia striata | X | | |China, Java,
| | | |Lombock
170. Calaenas nicobarica | X | | |Malacca and New
| | | |Guinea
| | | |
GALLINAE. | | | |
171. Gallus bankiva | X | | |Java, Timor
172. Coturnix minima | X | | |(Var. of _C.
| | | |Chinensis_)
173. Turnix rufilatus | X | | |
*174. ,, beccarii (Salv.) | X | | |
175. Megapodius gilberti | X | | |
176. Megacephalon malleo | X | | X |
| | | |
ACCIPITRES. | | | |
177. Circus assimilis | X | | |Australia
178. Astur griseiceps | X | | |
*179. ,, tenuirostris (Brugg.) X | | |
180. ,, rhodogastra | X | | |
181. ,, trinotata | X | | |
182. Accipiter sulaensis (Schl.) X | | |
183. ,, soloensis | X | | |Malacca & New
| | | |Guin.
184. Neopus malayensis | X | | |Nepaul, Sum.,
| | | |Java, Moluccas
185. Spizaetus lanceolatus | X | X | |
186. Haliactus leucogaster | X | | |Oriental region
187. Spilornis rufipectus | X | X | |
188. Butastur liventer | X | | |Java, Timor
189. ,, indicus | X | | X |India, Java
190. Haliastur leucosternus | X | | |Moluccas, New
| | | |Guin.
191. Milvus affinis | X | | |Australia
192. Elanus hypoleucus | X | | |? Java, Borneo
193. Pernis ptilorhyncha (var. | | | |
celebensis) | X | | |(Var. Java, &c.)
194. Baza erythrothorax | X | X | |
195. Falco severus | X | | |All Archipel.
196. Cerchneis moluccensis | X | | |Java, Moluccas
197. Polioaetus humilis | X | | |India, Malaya
| | | |
STRIGIDAE. | | | |
198. Athene punctulata | X | | |
199. ,, ochracea | X | | |
200. Scops magicus | X | | |Amboyna, &c.?
201. ,, menadensis | X | | |Flores,
| | | |Madagascar
202. Ninox japonicus | X | | |China, Japan
*203. ,, scutulata | | | X |Malacca
| | |(Salv.)|
204. Strix rosenbergi | X | | |
--------------------------------+-------+-------+-------+--------------------
* * * * *
{471}
CHAPTER XXI
ANOMALOUS ISLANDS: NEW ZEALAND
Position and Physical Features of New Zealand--Zoological Character of
New Zealand--Mammalia--Wingless Birds Living and Extinct--Recent
Existence of the Moa--Past Changes of New Zealand deduced from its
Wingless Birds--Birds and Reptiles of New Zealand--Conclusions from the
Peculiarities of the New Zealand Fauna.
The fauna of New Zealand has been so recently described, and its bearing on
the past history of the islands so fully discussed in my large work already
referred to, that it would not be necessary to introduce the subject again,
were it not that we now approach it from a somewhat different point of
view, and with some important fresh material, which will enable us to
arrive at more definite conclusions as to the nature and origin of this
remarkable fauna and flora. The present work is, besides, addressed to a
wider class of readers than my former volumes, and it would be manifestly
incomplete if all reference to one of the most remarkable and interesting
of insular faunas was omitted.
The two great islands which mainly constitute New Zealand are together
about as large as the kingdom of Italy. They stretch over thirteen degrees
of latitude in the warmer portion of the south-temperate zone, their
extreme points corresponding to the latitudes of Vienna and Cyprus. Their
climate throughout is mild and {472} equable, their vegetation is
luxuriant, and deserts or uninhabitable regions are as completely unknown
as in our own islands.
The geological structure of these islands has a decidedly continental
character. Ancient sedimentary rocks, granite, and modern volcanic
formations abound; gold, silver, copper, tin, iron, and coal are plentiful;
and there are also some considerable deposits of early or late Tertiary
age. The Secondary rocks alone are very scantily developed, and such
fragments as exist are chiefly of Cretaceous age, often not clearly
separated from the succeeding Eocene beds.
[Illustration: MAP SHOWING DEPTHS OF SEA AROUND AUSTRALIA AND NEW ZEALAND.]
The light tint indicates a depth of less than 1,000 fathoms.
The dark tint ,, ,, more than 1,000 fathoms.
The position of New Zealand, in the great Southern Ocean, about 1,200 miles
distant from the Australian {473} continent, is very isolated. It is
surrounded by a moderately deep ocean; but the form of the sea-bottom is
peculiar, and may help us in the solution of some of the anomalies
presented by its living productions. The line of 200 fathoms encloses the
two islands and extends their area considerably; but the 1,000-fathom line,
which indicates the land-area that would be produced if the sea-bottom were
elevated 6,000 feet, has a very remarkable conformation, extending in a
broad mass westward and northward, then sending out a great arm reaching to
beyond Lord Howe's Island. Norfolk Island is situated on a moderate-sized
bank, while two others, much more extensive, to the north-west approach the
great barrier reef, which here carries the 1,000-fathom line more than 300
miles from the coast. It is probable that a bank, less than 1,500 fathoms
below the surface, extends over this area, thus forming a connection with
tropical Australia and New Guinea. Temperate Australia, on the other hand,
is divided from New Zealand by an oceanic gulf about 700 miles wide and
between 2,000 and 3,000 fathoms deep. The 2,000-fathom line embraces all
the islands immediately round New Zealand as far as the Fijis to the north,
while a submarine plateau at a depth somewhere between one and two thousand
fathoms stretches southward to the Antarctic continent. Judging from these
indications, we should say that the most probable ancient connections of
New Zealand were with tropical Australia, New Caledonia, and the Fiji
Islands, and perhaps at a still more remote epoch, with the great Southern
continent by means of intervening lands and islands; and we shall find that
a land-connection or near approximation in these two directions, at remote
periods, will serve to explain many of the remarkable anomalies which these
islands present.
_Zoological Character of New Zealand._--We see, then, that both
geologically and geographically New Zealand has more of the character of a
"continental" than of an "oceanic" island, yet its zoological
characteristics are such as almost to bring it within the latter
category--and it is this which gives it its anomalous character. It is
usually {474} considered to possess no indigenous mammalia; it has no
snakes, and only one frog; it possesses (living or quite recently extinct)
an extensive group of birds incapable of flight; and its productions
generally are wonderfully isolated, and seem to bear no predominant or
close relation to those of Australia or any other continent. These are the
characteristics of an oceanic island; and thus we find that the inferences
from its physical structure and those from its forms of life directly
contradict each other. Let us see how far a closer examination of the
latter will enable us to account for this apparent contradiction.
_Mammalia of New Zealand._--The only undoubtedly indigenous mammalia appear
to be two species of bats, one of which (_Scotophilus tuberculatus_) is,
according to Mr. Dobson, identical with an Australian form, while the other
(_Mystacina tuberculata_) forms a very remarkable and isolated genus of
Emballonuridae, a family which extends throughout all the tropical regions
of the globe. The genus Mystacina was formerly considered to belong to the
American Phyllostomidae, but this has been shown to be an error.[117] The
poverty of New Zealand in bats is very remarkable when compared with our
own islands where there are at least twelve distinct species, though we
have a far less favourable climate.
Of the existence of truly indigenous land mammals in New Zealand there is
at present no positive evidence, but there is some reason to believe that
one if not two species may be found there. The Maoris say that before
Europeans came to their country a forest-rat abounded and was largely used
for food. They believe that their ancestors brought it with them when they
first came to the country; but it has now become almost, if not quite,
exterminated by the European brown rat. What this native animal was is
still somewhat doubtful. Several specimens have been caught at different
times which have been declared by the natives to be the true _Kiore
Maori_--as they term it, but these have usually proved on examination to be
either the European black rat or some of the native Australian rats which
now {475} often find their way on board ships. But within the last few
years many skulls of a rat have been obtained from the old Maori
cooking-places, and from a cave associated with moa bones; and Captain
Hutton, who has examined them, states that they belong to a true Mus, but
differ from the _Mus rattus_. This animal might have been on the islands
when the Maoris first arrived, and in that case would be truly indigenous;
while the Maori legend of their "ancestors" bringing the rat from their
Polynesian home may be altogether a myth invented to account for its
presence in the islands, because the only other land mammal which they
knew--the dog--was certainly so brought. The question can only be settled
by the discovery of remains of a rat in some deposit of an age decidedly
anterior to the first arrival of the Maori race in New Zealand.[118]
Much more interesting is the reported existence in the mountains of the
South Island of a small otter-like animal. Dr. Haast has seen its tracks,
resembling those of our European otter, at a height of 3,000 feet above the
sea in a region never before trodden by man; and the animal itself was seen
by two gentlemen near Lake Heron, about seventy miles due west of
Christchurch. It was described as being dark brown and the size of a large
rabbit. On being struck at with a whip, it uttered a shrill yelping sound
and disappeared in the water.[119] An animal seen so closely as to be
struck at with a whip could hardly have been mistaken for a dog--the only
other animal that it could possibly be supposed to have been, and a dog
would certainly not have "disappeared in the water." This account, as well
as the footsteps, point to an aquatic animal; and if it now frequents only
the high alpine lakes and streams, this might explain why it has never yet
been captured. Hochstetter also states that it has a native
name--Waitoteke--a striking evidence of its actual existence, while a
gentleman who lived many years in the district assures me that {476} it is
universally believed in by residents in that part of New Zealand. The
actual capture of this animal and the determination of its characters and
affinities could not fail to aid us greatly in our speculations as to the
nature and origin of the New Zealand fauna.[120]
_Wingless Birds, Living and Extinct._--Almost equally valuable with
mammalia in affording indications of geographical changes are the wingless
birds for which New Zealand is so remarkable. These consist of four species
of Apteryx, called by the natives "kiwis,"--creatures which hardly look
like birds owing to the apparent absence (externally) of tail or wings and
the dense covering of hair-like feathers. They vary in size from that of a
small fowl up to that of a turkey, and have a long slightly curved bill,
somewhat resembling that of the snipe or ibis. Two species appear to be
confined to the South Island, and one to the North Island, but all are
becoming scarce, and they will no doubt gradually become extinct. These
birds are generally classed with the Struthiones or ostrich tribe, but they
form a distinct family, and in many respects differ greatly from all other
known birds.
But besides these, a number of other wingless birds, called "moas,"
inhabited New Zealand during the period of human occupation, and have only
recently become extinct. These were much larger birds than the kiwis, and
some of them were even larger than the ostrich, a specimen {477} of
_Dinornis maximus_ mounted in the British Museum in its natural attitude
being eleven feet high. They agreed, however, with the living Apteryx in
the character of the pelvis and some other parts of the skeleton, while in
their short bill and in some important structural features they resembled
the emu of Australia and the cassowaries of New Guinea.[121] No less than
eleven distinct species of these birds have now been discovered; and their
remains exist in such abundance--in recent fluviatile deposits, in old
native cooking places, and even scattered on the surface of the
ground--that complete skeletons of several of them have been put together,
illustrating various periods of growth from the chick up to the adult bird.
Feathers have also been found attached to portions of the skin, as well as
the stones swallowed by the birds to assist digestion, and eggs, some
containing portions of the embryo bird; so that everything confirms the
statements of the Maoris--that their ancestors found these birds in
abundance on the islands, that they hunted them for food, and that they
finally exterminated them only a short time before the arrival of
Europeans.[122] Bones of Apteryx are also found fossil, but apparently of
the same species as the living birds. {478} How far back in geological time
these creatures or their ancestral types lived in New Zealand we have as
yet no evidence to show. Some specimens have been found under a
considerable depth of fluviatile deposits which may be of Quaternary or
even of Pliocene age; but this evidently affords us no approximation to the
time required for the origin and development of such highly peculiar
insular forms.
_Past Changes of New Zealand deduced from its Wingless Birds._--It has been
well observed by Captain Hutton, in his interesting paper already referred
to, that the occurrence of such a number of species of Struthious birds
living together in so small a country as New Zealand is altogether
unparalleled elsewhere on the globe. This is even more remarkable when we
consider that the species are not equally divided between the two islands,
for remains of no less than ten out of the eleven known species of Dinornis
have been found in a single swamp in the South Island, where also three of
the species of Apteryx occur. The New Zealand Struthiones, in fact, very
nearly equal in number those of all the rest of the world, and nowhere else
do more than three species occur in any one continent or island, while no
more than two ever occur in the same district. Thus, there appear to be two
closely allied species of ostriches inhabiting Africa and South-western
Asia respectively. South America has three species of Rhea, each in a
separate district. Australia has an eastern and a western variety of emu,
and a cassowary in the north; while eight other cassowaries are known from
the islands north of Australia--one from Ceram, two from the Aru Islands,
one from Jobie, one from New Britain, and three from New Guinea--but of
these last one is confined to the northern and another to the southern part
of the island.
This law, of the distribution of allied species in separate areas--which is
found to apply more or less accurately to all classes of animals--is so
entirely opposed to the crowding together of no less that fifteen species
of wingless birds in the small area of New Zealand, that the idea is at
once suggested of great geographical changes. Captain Hutton points out
that if the islands from Ceram to New Britain {479} were to become joined
together, we should have a large number of species of cassowary (perhaps
several more than are yet discovered) in one land area. If now this land
were gradually to be submerged, leaving a central elevated region, the
different species would become crowded together in this portion just as the
moas and kiwis were in New Zealand. But we also require, at some remote
epoch, a more or less complete union of the islands now inhabited by the
separate species of cassowaries, in order that the common ancestral form
which afterwards became modified into these species, could have reached the
places where they are now found; and this gives us an idea of the complete
series of changes through which New Zealand is believed to have passed in
order to bring about its abnormally dense population of wingless birds.
First, we must suppose a land connection with some country inhabited by
struthious birds, from which the ancestral forms might be derived;
secondly, a separation into many considerable islands, in which the various
distinct species might become differentiated; thirdly, an elevation
bringing about the union of these islands to unite the distinct species in
one area; and fourthly, a subsidence of a large part of the area, leaving
the present islands with the various species crowded together.
If New Zealand has really gone through such a series of changes as here
suggested, some proofs of it might perhaps be obtained in the outlying
islands which were once, presumably, joined with it. And this gives great
importance to the statement of the aborigines of the Chatham Islands, that
the Apteryx formerly lived there but was exterminated about 1835. It is to
be hoped that some search will be made here and also in Norfolk Island, in
both of which it is not improbable remains either of Apteryx or Dinornis
might be discovered.
So far we find nothing to object to in the speculations of Captain Hutton,
with which, on the contrary, we almost wholly concur; but we cannot follow
him when he goes on to suggest an Antarctic continent uniting New Zealand
and Australia with South America, and probably also with South Africa, in
order to explain the existing distribution {480} of struthious birds. Our
best anatomists, as we have seen, agree that both Dinornis and Apteryx are
more nearly allied to the cassowaries and emus than to the ostriches and
rheas; and we see that the form of the sea-bottom suggests a former
connection with North Australia and New Guinea--the very region where these
types most abound, and where in all probability they originated. The
suggestion that all the struthious birds of the world sprang from a common
ancestor at no very remote period, and that their existing distribution is
due to direct land communication between the countries they _now_ inhabit,
is one utterly opposed to all sound principles of reasoning in questions of
geographical distribution. For it depends upon two assumptions, both of
which are at least doubtful, if not certainly false--the first, that their
distribution over the globe has never in past ages been very different from
what it is now; and the second, that the ancestral forms of these birds
never had the power of flight. As to the first assumption, we have found in
almost every case that groups now scattered over two or more continents
formerly lived in intervening areas of existing land. Thus the marsupials
of South America and Australia are connected by forms which lived in North
America and Europe; the camels of Asia and the llamas of the Andes had many
extinct common ancestors in North America; the lemurs of Africa and Asia
had their ancestors in Europe, as had the trogons of South America, Africa,
and tropical Asia. But besides this general evidence we have direct proof
that the struthious birds had a wider range in past times than now. Remains
of extinct rheas have been found in Central Brazil, and those of ostriches
in North India; while remains, believed to be of struthious birds, are
found in the Eocene deposits of England; and the Cretaceous rocks of North
America have yielded the extraordinary toothed bird, Hesperornis, which
Professor O. Marsh declares to have been "a carnivorous swimming ostrich."
As to the second point, we have the remarkable fact that all known birds of
this group have not only the rudiments of wing-bones, but also the
rudiments of wings, that is, an external limb bearing rigid quills or
largely-developed {481} plumes. In the cassowary these wing-feathers are
reduced to long spines like porcupine-quills, while even in the Apteryx,
the minute external wing bears a series of nearly twenty stiff quill-like
feathers.[123] These facts render it almost certain that the struthious
birds do not owe their imperfect wings to a direct evolution from a
reptilian type, but to a retrograde development from some low form of
winged birds, analogous to that which has produced the dodo and the
solitaire from the more highly-developed pigeon-type. Professor Marsh has
proved, that so far back as the Cretaceous period, the two great forms of
birds--those with a keeled sternum and fairly-developed wings, and those
with a convex keel-less sternum and rudimentary wings--already existed side
by side; while in the still earlier Archaeopteryx of the Jurassic period we
have a bird with well-developed wings, and therefore probably with a keeled
sternum. We are evidently, therefore, very far from a knowledge of the
earliest stages of bird life, and our acquaintance with the various forms
that have existed is scanty in the extreme; but we may be sure that birds
acquired wings, and feathers, and some power of flight, before they
developed a keeled sternum, since we see that bats with no such keel fly
very well. Since, therefore, the struthious birds all have perfect
feathers, and all have rudimentary wings, which are anatomically those of
true birds, not the rudimentary fore-legs of reptiles, and since we know
that in many higher groups of birds--as the pigeons and the rails--the
wings have become more or less aborted, and the keel of the sternum greatly
reduced in size by disuse, it seems probable that the very remote ancestors
of the rhea, the cassowary, and the apteryx, were true flying birds,
although not perhaps provided with a keeled sternum, or possessing very
great powers of flight. But in addition to the possible ancestral power of
flight, we have the undoubted fact that the rhea and the emu both swim
freely, the former having been seen swimming from island to island off the
coast of Patagonia. This, taken in connection with the wonderful aquatic
ostrich of the Cretaceous period discovered by Professor Marsh, opens {482}
up fresh possibilities of migration; while the immense antiquity thus given
to the group and their universal distribution in past time, renders all
suggestions of special modes of communication between the parts of the
globe in which their scattered remnants _now_ happen to exist, altogether
superfluous and misleading.
The bearing of this argument on our present subject is, that so far as
accounting for the presence of wingless birds in New Zealand is concerned,
we have nothing whatever to do with any possible connection, by way of a
southern continent or antarctic islands, with South America and South
Africa, because the nearest allies of its moas and kiwis are the
cassowaries and emus, and we have distinct indications of a former land
extension towards North Australia and New Guinea, which is exactly what we
require for the original entrance of the struthious type into the New
Zealand area.
_Winged Birds and Lower Vertebrates of New Zealand._--Having given a pretty
full account of the New Zealand fauna elsewhere[124] I need only here point
out its bearing on the hypothesis now advanced, of the former
land-connection having been with North Australia, New Guinea, and the
Western Pacific Islands, rather than with the temperate regions of
Australia.
Of the Australian genera of birds, which are found also in New Zealand,
almost every one ranges also into New Guinea or the Pacific Islands, while
the few that do not extend beyond Australia are found in its northern
districts. As regards the peculiar New Zealand genera, all whose affinities
can be traced are allied to birds which belong to the tropical parts of the
Australian region; while the starling family, to which four of the most
remarkable New Zealand birds belong (the genera Creadion, Heterolocha, and
Callaeas), is totally wanting in temperate Australia and is comparatively
scarce in the entire Australian region, but is abundant in the Oriental
region, with which New Guinea and the Moluccas are in easy communication.
It is certainly a most suggestive fact that there are more than sixty {483}
genera of birds peculiar to the Australian continent (with Tasmania), many
of them almost or quite confined to its temperate portions, and that no
single one of these should be represented in temperate New Zealand.[125]
The affinities of the living and more highly organised, no less than those
of the extinct and wingless birds, strikingly accord with the line of
communication indicated by the deep submarine bank connecting these
temperate islands with the tropical parts of the Australian region.
The reptiles, so far as they go, are quite in accordance with the birds.
The lizards belong to two genera, Lygosoma, which has a wide range in all
the tropics as well as in Australia; and Naultinus, a genus peculiar to New
Zealand, but belonging to a family--Geckonidae--spread over the whole of
the warmer parts of the world. Australia, with New Guinea, on the other
hand, has a peculiar family, and no less than twenty-one peculiar genera of
lizards, many of which are confined to its temperate regions, but no one of
them extends to temperate New Zealand.[126] The extraordinary lizard-like
_Hatteria punctata_ of New Zealand forms of itself a distinct order of
reptiles, in some respects intermediate between lizards and crocodiles, and
having therefore no affinity with any living animal.
The only representative of the Amphibia in New Zealand is a solitary frog
of a peculiar genus (_Liopelma hochstetteri_); but it has no affinity for
any of the Australian frogs, which are numerous, and belong to eleven
different families; while the Liopelma belongs {484} to a very distinct
family (Discoglossidae), confined to the Palaearctic region.
Of the fresh-water fishes we need only say here, that none belong to
peculiar Australian types, but are related to those of temperate South
America or of Asia.
The Invertebrate classes are comparatively little known, and their modes of
dispersal are so varied and exceptional that the facts presented by their
distribution can add little weight to those already adduced. We will,
therefore, now proceed to the conclusions which can fairly be drawn from
the general facts of New Zealand natural history already known to us.
_Deductions from the Peculiarities of the New Zealand Fauna._--The total
absence (or extreme scarcity) of mammals in New Zealand obliges us to place
its union with North Australia and New Guinea at a very remote epoch. We
must either go back to a time when Australia itself had not yet received
the ancestral forms of its present marsupials and monotremes, or we must
suppose that the portion of Australia with which New Zealand was connected
was then itself isolated from the mainland, and was thus without a
mammalian population. We shall see in our next chapter that there are
certain facts in the distribution of plants, no less than in the geological
structure of the country, which favour the latter view. But we must on any
supposition place the union very far back, to account for the total want of
identity between the winged birds of New Zealand and those peculiar to
Australia, and a similar want of accordance in the lizards, the fresh-water
fishes, and the more important insect-groups of the two countries. From
what we know of the long geological duration of the generic types of these
groups we must certainly go back to the earlier portion of the Tertiary
period at least, in order that there should be such a complete disseverance
as exists between the characteristic animals of the two countries; and we
must further suppose that, since their separation, there has been no
subsequent union or sufficiently near approach to allow of any important
intermigration, even of winged birds, between them. It seems probable,
therefore, that {485} the Bampton shoal west of New Caledonia, and Lord
Howe's Island further south, formed the western limits of that extensive
land in which the great wingless birds and other isolated members of the
New Zealand fauna were developed. Whether this early land extended eastward
to the Chatham Islands and southward to the Macquaries we have no means of
ascertaining, but as the intervening sea appears to be not more than about
1,500 fathoms deep it is quite possible that such an amount of subsidence
may have occurred. It is possible, too, that there may have been an
extension northward to the Kermadec Islands, and even further to the Tonga
and Fiji Islands, though this is hardly probable, or we should find more
community between their productions and those of New Zealand.
A southern extension towards the Antarctic continent at a somewhat later
period seems more probable, as affording an easy passage for the numerous
species of South American and Antarctic plants, and also for the identical
and closely allied fresh-water fishes of these countries.
The subsequent breaking up of this extensive land into a number of separate
islands in which the distinct species of moa and kiwi were developed--their
union at a later period, and the final submergence of all but the existing
islands, is a pure hypothesis, which seems necessary to explain the
occurrence of so many species of these birds in a small area but of which
we have no independent proof. There are, however, some other facts which
would be explained by it, as the presence of three peculiar but allied
genera of starlings, the three species of parrots of the genus Nestor, and
the six distinct rails of the genus Ocydromus, as well as the numerous
species in some of the peculiar New Zealand genera of plants, which seem
less likely to have been developed in a single area than when isolated, and
thus preserved from the counteracting influence of intercrossing.
In the present state of our knowledge these seem all the conclusions we can
arrive at from a study of the New Zealand fauna; but as we fortunately
possess a tolerably {486} full and accurate knowledge of the flora of New
Zealand, as well as of that of Australia and the south temperate lands
generally, it will be well to see how far these conclusions are supported
by the facts of plant distribution, and what further indications they
afford us of the early history of these most interesting countries. This
inquiry is of sufficient importance to occupy a separate chapter.
* * * * *
{487}
CHAPTER XXII
THE FLORA OF NEW ZEALAND: ITS AFFINITIES AND PROBABLE ORIGIN
Relations of the New Zealand Flora to that of Australia--General
Features of the Australian Flora--The Floras of South-eastern and
South-western Australia--Geological Explanation of the Differences of
these two Floras--The Origin of the Australian Element in the New
Zealand Flora--Tropical Character of the New Zealand Flora
Explained--Species Common to New Zealand and Australia mostly Temperate
Forms--Why Easily Dispersed Plants have often Restricted
Ranges--Summary and Conclusion on the New Zealand Flora.
Although plants have means of dispersal far exceeding those possessed by
animals, yet as a matter of fact comparatively few species are carried for
very great distances, and the flora of a country taken as a whole usually
affords trustworthy indications of its past history. Plants, too, are more
numerous in species than the higher animals, and are almost always better
known; their affinities have been more systematically studied; and it may
be safely affirmed that no explanation of the origin of the fauna of a
country can be sound, which does not also explain, or at least harmonise
with, the distribution and relations of its flora. The distribution of the
two may be very different, but both should be explicable by the same series
of geographical changes.
The relations of the flora of New Zealand to that of Australia have long
formed an insoluble enigma for {488} botanists. Sir Joseph Hooker, in his
most instructive and masterly essay on the flora of Australia,
says:--"Under whatever aspect I regard the flora of Australia and of New
Zealand, I find all attempts to theorise on the possible causes of their
community of feature frustrated by anomalies in distribution, such as I
believe no two other similarly situated countries in the globe present.
Everywhere else I recognise a parallelism or harmony in the main common
features of contiguous floras, which conveys the impression of their
generic affinity, at least, being affected by migration from centres of
dispersion in one of them, or in some adjacent country. In this case it is
widely different. Regarding the question from the Australian point of view,
it is impossible in the present state of science to reconcile the fact of
Acacia, Eucalyptus, Casuarina, Callitris, &c., being absent in New Zealand,
with any theory of transoceanic migration that may be adopted to explain
the presence of other Australian plants in New Zealand; and it is very
difficult to conceive of a time or of conditions that could explain these
anomalies, except by going back to epochs when the prevalent botanical as
well as geographical features of each were widely different from what they
are now. On the other hand, if I regard the question from the New Zealand
point of view, I find such broad features of resemblance, and so many
connecting links that afford irresistible evidence of a close botanical
connection, that I cannot abandon the conviction that these great
differences will present the least difficulties to whatever theory may
explain the whole case." I will now state, as briefly as possible, what are
the facts above referred to as being of so anomalous a character, and there
is little difficulty in doing so, as we have them fully set forth, with
admirable clearness, in the essay above alluded to, and in the same
writer's _Introduction to the Flora of New Zealand_, only requiring some
slight modifications, owing to the later discoveries which are given in the
_Handbook of the New Zealand Flora_.
Confining ourselves always to flowering plants, we find that the flora of
New Zealand is a very poor one, considering the extent of surface, and the
favourable conditions of {489} soil and climate. It consists of 1,085
species (our own islands possessing about 1,500), but a very large
proportion of these are peculiar, there being no less than 800 endemic
species, and thirty-two endemic genera.
Out of the 285 species not peculiar to New Zealand, no less than 215 are
Australian, but a considerable number of these are also Antarctic, South
American, or European; so that there are only about 100 _species_
absolutely confined to New Zealand and Australia, and, what is important as
indicating a somewhat recent immigration, only some half-dozen of these
belong to _genera_ which are peculiar to the two countries, and hardly any
to the larger and more important Australian genera. Many, too, are rare
species in both countries and are often alpines.
Far more important are the relations of the genera and families of the two
countries. All the Natural Orders of New Zealand are found in Australia
except three--Coriariae, a widely-scattered group found in South Europe,
the Himalayas, and the Andes; Escallonieae, a widely distributed group; and
Chloranthaceae, found in Tropical Asia, Japan, Polynesia, and South
America. Out of a total of 310 New Zealand genera, no less than 248 are
Australian, and sixty of these are almost peculiar to the two countries,
only thirty-two however being absolutely confined to them.[127] In the
three large orders--Compositae, Orchideae, and Gramineae, the genera are
almost identical in the two countries, while the species--in the two former
especially--are mostly distinct.
Here then we have apparently a wonderful resemblance between the New
Zealand flora and that of Australia, indicated by more than two-thirds of
the non-peculiar species, and more than nine-tenths of the non-peculiar
genera (255) being Australian. But now let us look at the other side of the
question.
There are in Australia seven great genera of plants, each containing more
than 100 species, all widely spread over {490} the country, and all highly
characteristic Australian forms,--Acacia, Eucalyptus, Melaleuca,
Leucopogon, Stylidium, Grevillea, and Hakea. These are entirely absent from
New Zealand, except one species of Leucopogon, a genus which also has
representatives in the Malayan and Pacific Islands. Sixteen more Australian
genera have over fifty species each, and of these eight are totally absent
from New Zealand, five are represented by one or two species, and only two
are fairly represented; but these two--Drosera and Helichrysum--are very
widespread genera, and might have reached New Zealand from other countries
than Australia.
But this by no means exhausts the differences between New Zealand and
Australia. No less than seven Australian Natural Orders--Dilleniaceae,
Buettneriaceae, Polygaleae, Tremandreae, Casuarineae, Haemodoraceae, and
Xyrideae are entirely wanting in New Zealand, and several others which are
excessively abundant and highly characteristic of the former country are
very poorly represented in the latter. Thus, Leguminosae are extremely
abundant in Australia, where there are over 1,000 species belonging to
about 100 genera, many of them altogether peculiar to the country; yet in
New Zealand this great order is most scantily represented, there being only
five genera and thirteen species; and only two of these genera, Swainsonia
and Clianthus, are Australian, and as the latter consists of but two
species it may as well have passed from New Zealand to Australia as the
other way, or more probably from some third country to them both.[128]
Goodeniaceae with ten genera and 220 species Australian, has but two
species in New Zealand--and one of these is a salt-marsh plant found also
in Tasmania and in Chile; and four other large Australian orders--Rhamneae,
Myoporineae, Proteaceae and Santalaceae, have very few representatives in
New Zealand.
We find, then, that the great fact we have to explain and account for is,
the undoubted affinity of the New {491} Zealand flora to that of Australia,
but an affinity almost exclusively confined to the least predominant and
least peculiar portion of that flora, leaving the most predominant, most
characteristic, and most widely distributed portion absolutely
unrepresented. We must however be careful not to exaggerate the amount of
affinity with Australia, apparently implied by the fact that nearly
six-sevenths of the New Zealand genera are also Australian, for, as we have
already stated, a very large number of these are European, Antarctic, South
American or Polynesian genera, whose presence in the two contiguous areas
only indicates a common origin. About one-eighth, only, are absolutely
confined to Australia and New Zealand (thirty-two genera), and even of
these several are better represented in New Zealand than in Australia, and
may therefore have passed from the former to the latter. No less than 174
of the New Zealand genera are temperate South American, many being also
Antarctic or European; while others again are especially tropical or
Polynesian; yet undoubtedly a larger proportion of the Natural Orders and
genera are common to Australia than to any other country, so that we may
say that the basis of the flora is Australian with a large intermixture of
northern and southern temperate forms and others which have remote
world-wide affinities.
_General Features of the Australian Flora and its Probable Origin._--Before
proceeding to point out how the peculiarities of the New Zealand flora may
be best accounted for, it is necessary to consider briefly what are the
main peculiarities of Australian vegetation, from which so important a part
of that of New Zealand has evidently been derived.
The actual Australian flora consists of two great divisions--a temperate
and a tropical, the temperate being again divisible into an eastern and a
western portion. All that is most characteristic of the Australian flora
belongs to the temperate division (though these often overspread the whole
continent), in which are found almost all the remarkable Australian types
of vegetation and the numerous genera peculiar to this part of the world.
Contrary to what occurs in most other countries, the {492} tropical appears
to be less rich in species and genera than the temperate region, and what
is still more remarkable it contains fewer peculiar species, and very few
peculiar genera. Although the area of tropical Australia is about equal to
that of the temperate portions, and it has now been pretty well explored
botanically, it has probably not more than half as many species.[129]
Nearly 500 of its species are identical with Indian or Malayan plants, or
are very close representatives of them; while there are more than 200
Indian genera, confined for the most part to the tropical portion of
Australia. The remainder of the tropical flora consists of a few species
and many genera of temperate {493} Australia which range over the whole
continent, but these form only a small portion of the peculiarly Australian
genera.
These remarkable facts clearly point to one conclusion--that the flora of
tropical Australia is, comparatively, recent and derivative. If we imagine
the greater part of North Australia to have been submerged beneath the
ocean, from which it rose in the middle or latter part of the Tertiary
period, offering an extensive area ready to be covered by such suitable
forms of vegetation as could first reach it, something like the present
condition of things would inevitably arise. From the north, widespread
Indian and Malay plants would quickly enter, while from the south the most
dominant forms of warm-temperate Australia, and such as were best adapted
to the tropical climate and arid soil, would intermingle with them. Even if
numerous islands had occupied the area of Northern Australia for long
periods anterior to the final elevation, very much the same state of things
would result.
The existence in North and North-east Australia of enormous areas covered
with Cretaceous and other Secondary deposits, as well as extensive Tertiary
formations, lends support to the view, that during very long epochs
temperate Australia was cut off from all close connection with the tropical
and northern lands by a wide extent of sea; and this isolation is exactly
what was required, in order to bring about the wonderful amount of
specialisation and the high development manifested by the typical
Australian flora. Before proceeding further, however, let us examine this
flora itself, so far as regards its component parts and probable past
history.
_The Floras of South-eastern and South-western Australia._--The
peculiarities presented by the south-eastern and south-western subdivisions
of the flora of temperate Australia are most interesting and suggestive,
and are, perhaps, unparalleled in any other part of the world. South-west
Australia is far less extensive than the south-eastern division--less
varied in soil and climate, with no lofty mountains, and much sandy desert;
yet, strange to say, it contains an equally rich flora and a far greater
proportion of peculiar species and genera of plants. As Sir {494} Joseph
Hooker remarks:--"What differences there are in conditions would, judging
from analogy with other countries, favour the idea that South-eastern
Australia, from its far greater area, many large rivers, extensive tracts
of mountainous country and humid forests, would present much the most
extensive flora, of which only the drier types could extend into
South-western Australia. But such is not the case; for though the far
greater area is much the best explored, presents more varied conditions,
and is tenanted by a larger number of Natural Orders and genera, these
contain fewer species by several hundreds."[130]
The fewer genera of South-western Australia are due almost wholly to the
absence of the numerous European, Antarctic, and South-American types found
in the south-eastern region, while in purely Australian types it is far the
richer, for while it contains most of those found in the east it has a
large number altogether peculiar to it; and Sir Joseph Hooker states that
"there are about 180 genera, out of 600 in South-western Australia, that
are either not found at all in South-eastern, or that are represented there
by a very few species only, and these 180 genera include nearly 1,100
species."
_Geological Explanation of the Differences of these Two Floras._--These
facts again clearly point to the conclusion that South-western Australia is
the remnant of the more extensive and more isolated portion of the
continent in which the peculiar Australian flora was principally developed.
The existence there of a very large area of granite--800 miles in length by
nearly 500 in maximum width with detached masses 200 miles to the north and
500 miles to the east--indicates such an extension; for these {495}
granitic masses were certainly once buried under piles of stratified rock,
since denuded, and then formed the nucleus of the old Western Australian
continent. If we take the 1000-fathom line around the southern part of
Australia to represent the probable extension of this old land we shall see
that it would give a wide additional area south of the Great Australian
Bight, and form a continent which, even if the greater part of tropical
Australia were submerged, would be sufficient for the development of a
peculiar and abundant flora. We must also remember that an elevation of
6000 feet, added to the vast amount which has been taken away by
denudation, would change the whole country, including what are now the
deserts of the interior, into a mountainous and well-watered region.
But while this rich and peculiar flora was in process of formation, the
eastern portion of the continent must either have been widely separated
from the western or had perhaps not yet risen from the ocean. The whole of
this part of the country consists of Palaeozoic and Secondary formations
with granite and metamorphic rocks, the Secondary deposits being largely
developed on both sides of the central range, extending the whole length of
the continent from Tasmania to Cape York, and constituting the greater part
of the plateau of the Blue Mountains and other lofty ranges. During some
portion of the Secondary and Tertiary periods therefore, this side of
Australia must have been almost wholly submerged beneath the ocean; and if
we suppose that during this time the western part of the continent was at
nearly its maximum extent and elevation, we shall have a sufficient
explanation of the great difference between the flora of Western and
Eastern Australia, since the latter would only have been able to receive
immigrants from the former, at a later period, and in a more or less
fragmentary manner.
If we examine the geological map of Australia (given in Stanford's
Compendium of Geography and Travel, volume _Australasia_), we shall see
good reason to conclude that the eastern and the western divisions of the
country first existed as separate islands, and only became united at a
comparatively recent epoch. This is indicated by an {496} enormous stretch
of Cretaceous and Tertiary formations extending from the Gulf of
Carpentaria completely across the continent to the mouth of the Murray
River. During the Cretaceous period, therefore, and probably throughout a
considerable portion of the Tertiary epoch,[131] there must have been a
wide arm of the sea occupying this area, dividing the great mass of land on
the west--the true seat and origin of the typical Australian flora--from a
long but narrow belt of land on the east, indicated by the continuous mass
of Secondary and Palaeozoic formations already referred to which extend
uninterruptedly from Tasmania to Cape York. Whether this formed one
continuous land, or was broken up into islands, cannot be positively
determined; but the fact that no marine Tertiary beds occur in the whole of
this area, renders it probable that it was almost, if not quite,
continuous, and that it not improbably extended across to what is now New
Guinea. At this epoch, then (as shown in the accompanying map), Australia
may, not improbably, have consisted of a very large and fertile western
island, almost or quite extratropical, and extending from the Silurian
rocks of the Flinders range in South Australia, to about 150 miles west of
the present west coast, and southward to about 350 miles south of the Great
Australian Bight. To the east of this, at a distance of from 250 to 400
miles, extended in a north and south direction a long but comparatively
narrow island, stretching from far south of Tasmania to New Guinea; while
the crystalline and Secondary formations of central North Australia
probably indicate the existence of one or more large islands in that
direction.
{497}
The white portions represent land; the shaded parts sea.
The existing land of Australia is shown in outline.]
The eastern and the western islands--with which we are now chiefly
concerned--would then differ considerably in their vegetation and animal
life. The western and more ancient land already possessed, in its main
features, the peculiar Australian flora, and also the ancestral forms of
its strange marsupial fauna, both of which it had probably received at some
earlier epoch by a temporary union with the Asiatic continent over what is
now the Java sea. Eastern Australia, on the other hand, possessed only the
rudiments of its existing mixed flora, derived from three distinct sources.
Some important fragments of the typical Australian vegetation had reached
it across the marine {498} strait, and had spread widely owing to the soil,
climate and general conditions being exactly suited to it: from the north
and north-east a tropical vegetation of Polynesian type had occupied
suitable areas in the north; while the extension southward of the Tasmanian
peninsula, accompanied, probably, as now, with lofty mountains, favoured
the immigration of south-temperate forms from whatever Antarctic lands or
islands then existed. This supposition is strikingly in harmony with what
is known of the ancient flora of this portion of Australia. In deposits
supposed to be of Eocene age in New South Wales and Victoria fossil plants
have been found showing a very different vegetation from that now existing.
Along with a few Australian types--such as Pittosporum, Knightia, and
Eucalyptus, there occur birches, alders, oaks, and beeches; while in
Tasmania in freshwater limestone, apparently of Miocene age, are found
willows, alders, birches, oaks, and beeches,[132] all except the latter
genus (Fagus) now quite extinct in Australia.[133] These temperate forms
probably indicate a more oceanic climate, cooler and moister than at
present. The union with Western Australia and the establishment of an arid
interior by modifying the climate may have led to the extinction of many of
these forms and their replacement by special Australian types more suited
to the new conditions.
At this time the marsupial fauna had not yet reached this eastern land,
which was, however, occupied in the north by some ancestral struthious
birds, which had entered it by way of New Guinea through some very ancient
continental extension, and of which the emu, the cassowaries, the extinct
Dromornis of Queensland, and the moas and kiwis of New Zealand, are the
modified descendants.
_The Origin of the Australian Element in the New Zealand Flora._--We have
now brought down the history of Australia, as deduced from its geological
structure and the main features of its existing and Tertiary flora, to the
period {499} when New Zealand was first brought into close connection with
it, by means of a great north-western extension of that country, which, as
already explained in our last chapter, is so clearly indicated by the form
of the sea bottom (See Map, p. 471). The condition of New Zealand previous
to this event is very obscure. That it had long existed as a more or less
extensive land is indicated by its ancient sedimentary rocks; while the
very small areas occupied by Jurassic and Cretaceous deposits, imply that
much of the present land was then also above the sea-level. The country had
probably at that time a scanty vegetation of mixed Antarctic and Polynesian
origin; but now, for the first time, it would be open to the free
immigration of such Australian types as were suitable to its climate, and
which _had already reached the tropical and sub-tropical portions of the
Eastern Australian island_. It is here that we obtain the clue to those
strange anomalies and contradictions presented by the New Zealand flora in
its relation to Australia, which have been so clearly set forth by Sir
Joseph Hooker, and which have so puzzled botanists to account for. But
these apparent anomalies cease to present any difficulty when we see that
the Australian plants in New Zealand were acquired, not directly, but, as
it were, at second hand, by union with an island which itself had as yet
only received a portion of its existing flora. And then, further
difficulties were placed in the way of New Zealand receiving such an
adequate representation of that portion of the flora which had reached East
Australia as its climate and position entitled it to, by the fact of the
union being, not with the temperate, but with the tropical and sub-tropical
portions of that island, so that only those groups could be acquired which
were less exclusively temperate, and had already established themselves in
the warmer portion of their new home.[134]
{500}
It is therefore no matter of surprise, but exactly what we should expect,
that the great mass of pre-eminently temperate Australian genera should be
absent from New Zealand, including the whole of such important families as,
Dilleniaceae, Tremandreae, Buettneriacae, Polygaleae, Casuarineae and
Haemodoraceae; while others, such as Rutaceae, Stackhousieae, Rhamneae,
Myrtaceae, Proteaceae, and Santalaceae, are represented by only a few
species. Thus, too, we can explain the absence of _all_ the peculiar
Australian Leguminosae; for these were still mainly confined to the great
western island, along with the peculiar Acacias and Eucalypti, which at a
later period spread over the whole continent. It is equally accordant with
the view we are maintaining, that among the groups which Sir Joseph Hooker
enumerates as "keeping up the features of extra tropical Australia in its
tropical quarter," several should have reached New Zealand, such as
Drosera, some Pittosporeae and Myoporineae, with a few Proteaceae,
Loganiaceae, and Restiaceae; for most of these are not only found in
tropical Australia, but also in the Malayan and Pacific islands.
_Tropical Character of the New Zealand Flora Explained._--In this origin of
the New Zealand fauna by a north-western route from North-eastern
Australia, we find also an explanation of the remarkable number of tropical
groups of plants found there: for though, as Sir Joseph Hooker has {501}
shown, a moist and uniform climate favours the extension of tropical forms
in the temperate zone, yet some means must be afforded them for reaching a
temperate island. On carefully going through the _Handbook_, and comparing
its indications with those of Bentham's _Flora Australiensis_, I find that
there are in New Zealand thirty-eight thoroughly tropical genera,
thirty-three of which are found in Australia--mostly in the tropical
portion of it, though a few are temperate, and these may have reached it
through New Zealand[135]. To these we must add thirty-two more genera,
which, though chiefly developed in temperate Australia, extend into the
tropical or sub-tropical portions of it, and may well have reached New
Zealand by the same route.
On the other hand we find but few New Zealand genera certainly derived from
Australia which are especially temperate, and it may be as well to give a
list of such as {502} do occur with a few remarks. They are sixteen in
number, as follows:--
1. Pennantia (1 sp.). This genus has a species in Norfolk Island,
indicating perhaps its former extension to the north-west.
2. Pomaderris (3 sp.). One _species_ inhabits Victoria and New Zealand,
indicating recent trans-oceanic migration.
3. Quintinia (2 sp.). This genus has winged seeds facilitating
migration.
4. Olearia (20 sp.). Seeds with pappus.
5. Craspedia (2 sp.). Seeds with pappus. Alpine; identical with
Australian species, and therefore of comparatively recent introduction.
6. Celmisia (25 sp.). Seeds with pappus. Only three Australian species,
two of which are identical with New Zealand forms, probably therefore
derived from New Zealand.
7. Ozothamnus (5 sp.). Seeds with pappus.
8. Epacris (4 sp.). Minute seeds. Some species are sub-tropical, and
they are all found in the northern (warmer) island of New Zealand.
9. Archeria (2 sp.). Minute seeds. A species common to E. Australia and
New Zealand.
10. Logania (3 sp.). Small seeds. Alpine plants.
11. Hedycarya (1 sp.).
12. Chiloglottis (1 sp.). Minute seeds. In Auckland Islands; alpine in
Australia.
13. Prasophyllum (1 sp.). Minute seeds. Identical with Australian
species, indicating recent transmission.
14. Orthoceras (1 sp.). Minute seeds. Identical with an Australian
species.
15. Alepyrum (1 sp.). Alpine, moss-like. An Antarctic type.
16. Dichelachne (3 sp.). Identical with Australian species. An awned
grass.
We thus see that there are special features in most of these plants that
would facilitate transmission across the sea between temperate Australia
and New Zealand, or to both from some Antarctic island; and the fact that
in several of them the species are absolutely identical shows that such
transmission has occurred in geologically recent times.
_Species Common to New Zealand and Australia Mostly Temperate Forms._--Let
us now take the _species_ which are common to New Zealand and Australia,
but found nowhere else, and which must therefore have passed from one
country to the other at a more recent period than the mass of _genera_ with
which we have hitherto been dealing. These are ninety-six in number, and
they present a striking contrast to the similarly restricted _genera_ in
being wholly temperate in character, the entire list presenting only a
{503} single species which is confined to sub-tropical East Australia--a
grass (_Apera arundinacea_) only found in a few localities on the New
Zealand coast.
Now it is clear that the larger portion, if not the whole, of these plants
must have reached New Zealand from Australia (or in a few cases Australia
from New Zealand), by transmission across the sea, because we know there
has been no actual land connection during the Tertiary period, as proved by
the absence of all the Australian mammalia, and almost all the most
characteristic Australian birds, insects, and plants. The form of the
sea-bed shows that the distance could not have been less than 600 miles,
even during the greatest extension of Southern New Zealand and Tasmania;
and we have no reason to suppose it to have been less, because in other
cases an equally abundant flora of identical species has reached islands at
a still greater distance--notably in the case of the Azores and Bermuda.
The character of the plants is also just what we should expect: for about
two-thirds of them belong to genera of world-wide range in the temperate
zones, such as Ranunculus, Drosera, Epilobium, Gnaphalium, Senecio,
Convolvulus, Atriplex, Luzula, and many sedges and grasses, whose
exceptionally wide distribution shows that they possess exceptional powers
of dispersal and vigour of constitution, enabling them not only to reach
distant countries, but also to establish themselves there. Another set of
plants belong to especially Antarctic or south temperate groups, such as
Colobanthus, Acaena, Gaultheria, Pernettya, and Muhlenbeckia, and these may
in some cases have reached both Australia and New Zealand from some now
submerged Antarctic island. Again, about one-fourth of the whole are alpine
plants, and these possess two advantages as colonisers. Their lofty
stations place them in the best position to have their seeds carried away
by winds; and they would in this case reach a country which, having derived
the earlier portion of its flora from the side of the tropics, would be
likely to have its higher mountains and favourable alpine stations to a
great extent unoccupied, or occupied by plants unable to compete with
specially adapted alpine groups. {504}
Fully one-third of the exclusively Australo-New Zealand species belong to
the two great orders of the sedges and the grasses; and there can be no
doubt that these have great facilities for dispersion in a variety of ways.
Their seeds, often enveloped in chaffy glumes, would be carried long
distances by storms of wind, and even if finally dropped into the sea would
have so much less distance to reach the land by means of surface currents;
and Mr. Darwin's experiments show that even cultivated oats germinated
after 100 days' immersion in sea-water. Others have hispid awns by which
they would become attached to the feathers of birds, and there is no doubt
this is an effective mode of dispersal. But a still more important point
is, probably, that these plants are generally, if not always,
wind-fertilised, and are thus independent of any peculiar insects, which
might be wanting in the new country.
_Why Easily-Dispersed Plants have often Restricted Ranges._--This last
consideration throws light on a very curious point, which has been noted as
a difficulty by Sir Joseph Hooker, that plants which have most clear and
decided powers of dispersal by wind or other means, have _not_ generally
the widest specific range; and he instances the small number of Compositae
common to New Zealand and Australia. But in all these cases it will, I
think, be found that although the _species_ have not a wide range the
_genera_ often have. In New Zealand, for instance, the Compositae are very
abundant, there being no less than 167 species, almost all belonging to
Australian genera, yet only about one-sixteenth of the whole are identical
in the two countries. The explanation of this is not difficult. Owing to
their great powers of dispersal, the Australian Compositae reached New
Zealand at a very remote epoch, and such as were adapted to the climate and
the means of fertilisation established themselves; but being highly
organised plants with great flexibility of organisation, they soon became
modified in accordance with the new conditions, producing many special
forms in different localities; and these, spreading widely, soon took
possession of all suitable stations. Henceforth immigrants from Australia
had to compete {505} with these indigenous and well-established plants, and
only in a few cases were able to obtain a footing; whence it arises that we
have many Australian types, but few Australian species, in New Zealand, and
both phenomena are directly traceable to the combination of great powers of
dispersal with a high degree of adaptability. Exactly the same thing occurs
with the still more highly specialised Orchideae. These are not
proportionally so numerous in New Zealand (thirty-eight species), and this
is no doubt due to the fact that so many of them require
insect-fertilisation often by a particular family or genus (whereas almost
any insect will fertilise Compositae), and insects of all orders are
remarkably scarce in New Zealand.[136] This would at once prevent the
establishment of many of the orchids which may have reached the islands,
while those which did find suitable fertilisers and other favourable
conditions would soon become modified into new species. It is thus quite
intelligible why only three species of orchids are identical in Australia
and New Zealand, although their minute and abundant seeds must be dispersed
by the wind almost as readily as the spores of ferns.
Another specialised group--the Scrophularineae--abounds in New Zealand,
where there are sixty-two species; but though almost all the genera are
Australian only three species are so. Here, too, the seeds are usually very
small, and the powers of dispersal great, as shown by several European
genera--Veronica, Euphrasia, and Limosella, being found in the southern
hemisphere.
Looking at the whole series of these Australo-New Zealand plants, we find
the most highly specialised groups--Compositae, Scrophularineae,
Orchideae--with a small proportion of identical species (one-thirteenth to
one twentieth), the less highly specialised--Ranunculaceae, Onagrariae and
Ericeae--with a higher proportion (one-ninth to one-sixth), and the least
specialised--Junceae, {506} Cyperaceae and Gramineae--with the high
proportion in each case of one-fourth. These nine are the most important
New Zealand orders which contain species common to that country and
Australia and confined to them; and the marked correspondence they show
between high specialisation and want of _specific_ identity, while the
_generic_ identity is in all cases approximately equal, points to the
conclusion that the means of diffusion are, in almost all plants ample,
when long periods of time are concerned, and that diversities in this
respect are not so important in determining the peculiar character of a
derived flora, as adaptability to varied conditions, great powers of
multiplication, and inherent vigour of constitution. This point will have
to be more fully discussed in treating of the origin of the Antarctic and
north temperate members of the New Zealand flora.
_Summary and Conclusion on the New Zealand Flora._--Confining ourselves
strictly to the direct relations between the plants of New Zealand and of
Australia, as I have done in the preceding discussion, I think I may claim
to have shown that the union between the two countries in the latter part
of the Secondary epoch at a time when Eastern Australia was widely
separated from Western Australia (as shown by its geological formation and
by the contour of the sea-bottom) does sufficiently account for all the
main features of the New Zealand flora. It shows why the basis of the flora
is fundamentally Australian both as regards orders and genera, for it was
due either to a direct land connection or a somewhat close approximation
between the two countries. It shows also why the great mass of typical
Australian forms are unrepresented, for the Australian flora is typically
_western_ and _temperate_, and New Zealand received its immigrants from the
_eastern_ island which had itself received only a fragment of this flora,
and from the _tropical_ end of this island, and thus could only receive
such forms as were not exclusively temperate in character. It shows,
further, why New Zealand contains such a very large proportion of tropical
forms, for we see that it derived the main portion of its flora directly
from the tropics. Again, this hypothesis shows us why, though {507} the
specially Australian _genera_ in New Zealand are largely tropical or
sub-tropical, the specially Australian _species_ are wholly temperate or
alpine; for these are comparatively recent arrivals, they must have
migrated across the sea in the temperate zone, and these temperate and
alpine forms are exactly such as would be best able to establish themselves
in a country already stocked mainly by tropical forms and their modified
descendants. This hypothesis further fulfils the conditions implied in Sir
Joseph Hooker's anticipation that--"these great differences (of the floras)
will present the least difficulties to whatever theory may explain the
whole case,"--for it shows that these differences are directly due to the
history and development of the Australian flora itself, while the
resemblances depend upon the most certain cause of all such broad
resemblances--close proximity or actual land connection.
One objection will undoubtedly be made to the above theory,--that it does
not explain why some species of the prominent Australian genera Acacia,
Eucalyptus, Melaleuca, Grevillea, &c., have not reached New Zealand in
recent times along with the other temperate forms that have established
themselves. But it is doubtful whether any detailed explanation of such a
negative fact is possible, while general explanations sufficient to cover
it are not wanting. Nothing is more certain than that numerous plants never
run wild and establish themselves in countries where they nevertheless grow
freely if cultivated; and the explanation of this fact given by Mr.
Darwin--that they are prevented doing so by the competition of better
adapted forms--is held to be sufficient. In this particular case, however,
we have some very remarkable evidence of the fact of their non-adaptation.
The intercourse between New Zealand and Europe has been the means of
introducing a host of common European plants,--more than 150 in number, as
enumerated at the end of the second volume of the _Handbook_; yet, although
the intercourse with Australia has probably been greater, only two or three
Australian plants have similarly established themselves. More remarkable
still, Sir Joseph Hooker states: {508} "I am informed that the late Mr.
Bidwell habitually scattered Australian seeds during his extensive travels
in New Zealand." We may be pretty sure that seeds of such excessively
common and characteristic groups as _Acacia_ and _Eucalyptus_ would be
among those so scattered, yet we have no record of any plants of these or
other peculiar Australian genera ever having been found wild, still less of
their having spread and taken possession of the soil in the way that many
European plants have done. We are, then, entitled to conclude that the
plants above referred to have not established themselves in New Zealand
(although their seeds may have reached it) because they could not
successfully compete with the indigenous flora which was already well
established and better adapted to the conditions of climate and of the
organic environment. This explanation is so perfectly in accordance with a
large body of well-known facts, including that which is known to every
one--how few of our oldest and hardiest garden plants ever run wild--that
the objection above stated will, I feel convinced, have no real weight with
any naturalists who have paid attention to this class of questions.
* * * * *
{509}
CHAPTER XXIII
ON THE ARCTIC ELEMENT IN SOUTH TEMPERATE FLORAS
European Species and Genera of Plants in the Southern
Hemisphere--Aggressive Power of the Scandinavian Flora--Means by which
Plants have Migrated from North to South--Newly moved Soil as Affording
Temporary Stations to Migrating Plants--Elevation and Depression of the
Snow-line as Aiding the Migration of Plants--Changes of Climate
Favourable to Migration--The Migration from North to South has been
long going on--Geological Changes as Aiding Migration--Proofs of
Migration by way of the Andes--Proofs of Migration by way of the
Himalayas and Southern Asia--Proofs of Migration by way of the African
Highlands--Supposed Connection of South Africa and Australia--The
Endemic Genera of Plants in New Zealand--The Absence of Southern Types
from the Northern Hemisphere--Concluding Remarks on the New Zealand and
South Temperate Floras.
We have now to deal with another portion of the New Zealand flora which
presents perhaps equal difficulties--that which appears to have been
derived from remote parts of the north and south temperate zones; and this
will lead us to inquire into the origin of the northern or Arctic element
in all the south temperate floras.
More than one-third of the entire number of New Zealand genera (115) are
found also in Europe, and even fifty-eight species are identical in these
remote parts of the world. Temperate South America has seventy-four genera
in common with New Zealand, and there are even eleven species identical in
the two countries, as well as thirty-two which are close allies or
representative species. {510} A considerable number of these northern or
Antarctic plants and many more which are representative species, are found
also in Tasmania and in the mountains of temperate Australia; and Sir
Joseph Hooker gives a list of thirty-eight species very characteristic of
Europe and Northern Asia, but almost or quite unknown in the warmer
regions, which yet reappear in temperate Australia. Other genera seem
altogether Antarctic--that is, confined to the extreme southern lands and
islands; and these often have representative species in Southern America,
Tasmania, and New Zealand, while others occur only in one or two of these
areas. Many north temperate genera also occur in the mountains of South
Africa. On the other hand, few if any of the peculiar Australian or
Antarctic types have spread northwards, except some of the former which
have reached the mountains of Borneo, and a few of the latter which spread
along the Andes to Mexico.
On these remarkable facts, of which I have given but the barest outline,
Sir Joseph Hooker makes the following suggestive observations:--
"When I take a comprehensive view of the vegetation of the Old World, I am
struck with the appearance it presents of there being a continuous current
of vegetation (if I may so fancifully express myself) from Scandinavia to
Tasmania; along, in short, the whole extent of that arc of the terrestrial
sphere which presents the greatest continuity of land. In the first place
Scandinavian genera, and even species, reappear everywhere from Lapland and
Iceland to the tops of the Tasmanian Alps, in rapidly diminishing numbers
it is true, but in vigorous development throughout. They abound on the Alps
and Pyrenees, pass on to the Caucasus and Himalayas, thence they extend
along the Khasia Mountains, and those of the peninsulas of India to those
of Ceylon and the Malayan Archipelago (Java and Borneo), and after a hiatus
of 30deg they appear on the Alps of New South Wales, Victoria, and
Tasmania, and beyond these again on those of New Zealand and the Antarctic
Islands, many of the species remaining unchanged throughout! It matters not
what the vegetation of the bases and flanks of these mountains may be; the
northern species may be {511} associated with alpine forms of Germanic,
Siberian, Oriental, Chinese, American, Malayan, and finally Australian, and
Antarctic types; but whereas these are all, more or less, local
assemblages, the Scandinavian asserts his prerogative of ubiquity from
Britain to beyond its antipodes."[137]
It is impossible to place the main facts more forcibly before the reader
than in the above striking passage. It shows clearly that this portion of
the New Zealand flora is due to wide-spread causes which have acted with
even greater effect in other south temperate lands, and that in order to
explain its origin we must grapple with the entire problem of the transfer
of the north temperate flora to the southern hemisphere. Taking, therefore,
the facts as given by Sir Joseph Hooker in the works already referred to, I
shall discuss the whole question broadly, and shall endeavour to point out
the general laws and subordinate causes that, in my opinion, have been at
work in bringing about the anomalous phenomena of distribution he has done
so much to make known and to elucidate.
_Aggressive Power of the Scandinavian Flora._--The first important fact
bearing upon this question is the wonderful aggressive and colonising power
of the Scandinavian flora, as shown by the way in which it establishes
itself in any temperate country to which it may gain access. About 150
species have thus established themselves in New Zealand, often taking
possession of large tracts of country; about the same number are found in
Australia, and nearly as many in the Atlantic states of America, where they
form the commonest weeds. Whether or not we accept Mr. Darwin's explanation
of this power as due to development in the most extensive land area of the
globe where competition has been most severe and long-continued, the fact
of the existence of this power remains, and we can see how important an
agent it must be in the formation of the floras of any lands to which these
aggressive plants have been able to gain access.
But not only are these plants pre-eminently capable of holding their own in
any temperate country in the world, but they also have exceptional powers
of migration and {512} dispersal over seas and oceans. This is especially
well shown by the case of the Azores, where no less than 400 out of a total
of 478 flowering plants are identical with European species. These islands
are more than 800 miles from Europe, and, as we have already seen in
Chapter XII., there is no reason for supposing that they have ever been
more nearly connected with it than they are now, since an extension of the
European coast to the 1,000-fathom line would very little reduce the
distance. Now it is a most interesting and suggestive fact that more than
half the European genera which occur in the Australian flora occur also in
the Azores, and in several cases even the species are identical in
both.[138] The importance of such a case as this cannot be exaggerated,
because it affords a demonstration of the power of the very plants in
question to pass over wide areas of sea, some no doubt wholly through the
air, carried by storms in the same way as the European birds and insects
which annually reach the Azores, others by floating on the waters, or by a
combination of the two methods; while some may have been carried by aquatic
birds, to whose feathers many seeds have the power of attaching themselves,
and some even in the stomachs of fruit or seed eating birds. We have in
such facts as these a complete disproof of the necessity for those great
changes of sea and land which are continually appealed to by those who
think land-connection the only efficient means of accounting for the
migration of animals or plants; but at the same time we do not neglect to
make the fullest use of such moderate changes as all the evidence at our
command leads us to believe have actually occurred, and especially of the
former existence of intermediate islands, so often indicated by shoals in
the midst of the deepest oceans.
_Means by which Plants have migrated from North to South._--But if plants
can thus pass in considerable numbers and variety over wide seas and
oceans, it must be yet more easy for them to traverse continuous areas of
land, whereever mountain-chains offer suitable stations at moderate {513}
intervals on which they might temporarily establish themselves. The
facilities afforded for the transmission of plants by mountains has hardly
received sufficient attention. The numerous land-slips, the fresh surfaces
of broken rock and precipice, the _debris_ of torrents, and the moraines
deposited by glaciers, afford numerous unoccupied stations on which
wind-borne seeds have a good chance of germinating. It is a well-known fact
that fresh surfaces of soil or rock, such as are presented by railway
cuttings and embankments, often produce plants strange to the locality,
which survive for a few years, and then disappear as the normal vegetation
gains strength and permanence.[139] But such a surface {514} will, in the
meantime, have acted as a fresh centre of dispersal; and thus a plant might
pass on step by step, by means of stations temporarily occupied, till it
reached a district {515} where, the general conditions being more
favourable, it was able to establish itself as a permanent member of the
flora. Such, generally speaking, was probably the process by which the
Scandinavian flora has made its way to the southern hemisphere; but it
could hardly have done so to any important extent without the aid of those
powerful causes explained in our eighth chapter--causes which acted as a
constantly recurrent motive-power to produce that "continuous current of
vegetation" from north to south across the whole width of the tropics
referred to by Sir Joseph Hooker. Those causes were, the repeated changes
{516} of climate which, during all geological time, appear to have occurred
in both hemispheres, culminating at rare intervals in glacial epochs, and
which have been shown to depend upon changes of excentricity of the earth's
orbit and the occurrence of summer or winter in _aphelion_, in conjunction
with the slower and more irregular changes of geographical conditions;
these combined causes acting chiefly through the agency of heat-bearing
oceanic currents, and of snow- and ice-collecting highlands. Let us now
briefly consider how such changes would act in favouring the dispersal of
plants.
_Elevation and Depression of the Snow Line as Aiding the Migration of
Plants._--We have endeavoured to show (in an earlier portion of this
volume) that wherever geographical or physical conditions were such as to
produce any considerable amount of perpetual snow, this would be increased
whenever a high degree of excentricity concurred with winter in _aphelion_,
and diminished during the opposite phase. On all mountain ranges,
therefore, which reached above the snow-line, there would be a periodical
increase and decrease of snow, and when there were extensive areas of
plateau at about the same level, the lowering of the snow-line might cause
such an increased accumulation of snow as to produce great glaciers and
ice-fields, such as we have seen occurred in South Africa during the last
period of high excentricity. But along with such depression of the line of
perpetual snow there would be a corresponding depression of the alpine and
sub-alpine zones suitable for the growth of an arctic and temperate
vegetation, and, what is perhaps more important, the depression would
necessarily produce a great _extension_ of the area of these zones on all
high mountains, because as we descend the average slopes become less
abrupt,--thus affording a number of new stations suitable for such
temperate plants as might first reach them. But just above and below the
snow-line is the area of most powerful disintegration and denudation, from
the alternate action of frost and sun, of ice and water; and thus the more
extended area would be subject to the constant occurrence of land-slips,
berg-falls, and floods, with their {517} accompanying accumulations of
_debris_ and of alluvial soil, affording innumerable stations in which
solitary wind-borne seeds might germinate and temporarily establish
themselves.
This lowering and rising of the snow-line each 10,500 years during periods
of high excentricity, would occur in the northern and southern hemispheres
alternately; and where there were high mountains within the tropics the two
would probably overlap each other, so that the northern depression would
make itself felt in a slight degree even across the equator some way into
the southern hemisphere, and _vice versa_; and even if the difference of
the height of perpetual snow at the two extremes did not average more than
a few hundred feet, this would be amply sufficient to supply the new and
unoccupied stations needful to facilitate the migration of plants. It is
well known that all great mountain ranges have undergone such fluctuations,
as proved by ice-marks below the present level of snow and ice.
But the differences of temperature in the two hemispheres caused by the sun
being in _perihelion_ in the winter of the one while it was in _aphelion_
during the same season in the other, would necessarily lead to increased
aerial and marine currents, as already explained; and whenever geographical
conditions were such as to favour the production of glaciation in any area
these effects would become more powerful, and would further aid in the
dispersal of the seeds of plants.
_Changes of Climate Favourable to Migration._--It is clear then, that
during periods when no glacial epochs were produced in the northern
hemisphere, and even when a mild climate extended over the whole polar
area, alternate changes of climate favouring the dispersal of plants would
occur on all high mountains, and with particular force on such as rise
above the snow-line. But during that long-continued, though comparatively
recent, phase of high excentricity which produced an extensive glaciation
in the northern hemisphere and local glaciations in the southern, these
risings and lowerings of the snow-line on all mountain ranges would have
been at a maximum, and {518} would have been increased by the depression of
the ocean which must have arisen from such a vast bulk of water being
locked up in land-ice, and which depression would have produced the same
effect as a general elevation of all the continents. At this time, too,
aerial currents would have attained their maximum of force in both
hemispheres; and this would greatly facilitate the dispersal of all
wind-borne seeds as well as of those carried in the plumage or in the
stomachs of birds, since we have seen, by the cases of the Azores and
Bermuda, how vastly the migratory powers of birds are increased by a stormy
atmosphere.
_Migration from North to South has been long going on._--Now, if each phase
of colder and warmer mountain-climate--each alternate depression and
elevation of the snow-line, only helped on the migration of a few species
some stages of the long route from the north to the south temperate
regions, yet, during the long course of the Tertiary period there might
well have arisen that representation of the northern flora in the southern
hemisphere which is now so conspicuous. For it is very important to remark
that it is not the existing flora alone that is represented, such as might
have been conveyed during the last glacial epoch only; but we find a whole
series of northern types evidently of varying degrees of antiquity, while
even some genera characteristic of the southern hemisphere appear to have
been originally derived from Europe. Thus Eucalyptus and Metrosideros have
been determined by Dr. Ettingshausen from their fruits in the Eocene beds
of Sheppey, while Pimelea, Leptomeria and four genera of Proteaceae have
been recognised by Professor Heer in the Miocene of Switzerland; and the
former writer has detected fifty-five Australian forms in the Eocene plant
beds of Haering (? Belgium).[140] Then we have such peculiar genera {519}
as Pachychladon and Notothlaspi of New Zealand said to have affinities with
Arctic plants, while Stilbocarpa--another peculiar New Zealand genus--has
its nearest allies in the Himalayan and Chinese Aralias. Following these
are a whole host of very distinct species of northern genera which may date
back to any part of the Tertiary period, and which occur in every south
temperate land. Then we have closely allied representative species of
European or Arctic plants; and, lastly, a number of identical species,--and
these two classes are probably due entirely to the action of the last great
glacial epoch, whose long continuance, and the repeated fluctuations of
climate with which it commenced and terminated, rendered it an agent of
sufficient power to have brought about this result.
Here, then, we have that constant or constantly recurrent process of
dispersal acting throughout long periods with varying power--that
"continuous current of vegetation" as it has been termed, which the facts
demand; and the extraordinary phenomenon of the species and genera of
European and even of Arctic plants being represented abundantly in South
America, Australia, and New Zealand, thus adds another to the long series
of phenomena which are rendered intelligible by frequent alternations of
warmer and colder climates in either hemisphere, culminating, at long
intervals and in favourable situations, in actual glacial epochs.
_Geological Changes as Aiding Migration._--It will be well also to notice
here, that there is another aid to dispersion dependent upon the changes
effected by denudation during the long periods included in the duration of
the species and genera of plants. A considerable number of {520} the plants
of the Miocene period of Europe were so much like existing species that
although they have generally received fresh names they may well have been
identical; and a large proportion of the vegetation during the whole
Tertiary period consisted of genera which are still living.[141] But from
what is now known of the rate of sub-aerial denudation, we are sure, that
during each division of this period many mountain chains must have been
considerably lowered, while we know that some of the existing ranges have
been greatly elevated. Ancient volcanoes, too, have been destroyed by
denudation, and new ones have been built up, so that we may be quite sure
that ample means for the transmission of temperate plants across the
tropics, may have existed in countries where they are now no longer to be
found. The great mountain masses of Guiana and Brazil, for example, must
have been far more lofty before the sedimentary covering was denuded from
their granitic bosses and metamorphic peaks, and may have aided the
southern migration of plants before the final elevation of the Andes. And
if Africa presents us with an example of a continent of vast antiquity, we
may be sure that its great central plateaux once bore far loftier mountain
ranges before they were reduced to their present condition by long ages of
denudation.
_Proofs of Migration by Way of the Andes._--We are now prepared to apply
the principles above laid down to the explanation of the character and
affinities of the various portions of the north temperate flora in the
southern hemisphere, and especially in Australia and New Zealand.
At the present time the only unbroken chain of highlands and mountains
connecting the Arctic and north temperate with the Antarctic lands is to be
found in the American continent, the only break of importance being the
comparatively low Isthmus of Panama, where there is {521} a distance of
about 300 miles occupied by rugged forest-clad hills, between the lofty
peaks of Veragua and the northern extremity of the Andes of New Grenada.
Such distances are, as we have already seen, no barrier to the diffusion of
plants; and we should accordingly expect that this great continuous
mountain-chain has formed the most effective agent in aiding the southward
migration of the Arctic and north temperate vegetation. We do find, in
fact, not only that a large number of northern genera and many species are
scattered all along this line of route, but that at the end of the long
journey, in Southern Chile and Fuegia, they have established themselves in
such numbers as to form an important part of the flora of those countries.
From the lists given in the works already referred to, it appears that
there are between sixty and seventy northern genera in Fuegia and Southern
Chile, while about forty of the species are absolutely identical with those
of Europe and the Arctic regions. Considering how comparatively little the
mountains of South Temperate America are yet known, this is a very
remarkable result, and it proves that the transmission of species must have
gone on up to comparatively recent times. Yet, as only a few of these
species are now found along the line of migration, we see that they only
occupied such stations temporarily; and we may connect their disappearance
with the passing away of the last glacial period which, by raising the
snow-line, reduced the area on which alone they could exist, and exposed
them to the competition of indigenous plants from the belt of country
immediately below them.
Now, just as these numerous species and genera have undoubtedly passed
along the great American range of mountains, although only now found at its
two extremes, so others have doubtless passed on further; and have found
more suitable stations or less severe competition in the Antarctic
continent and islands, in New Zealand, in Tasmania, and even in Australia
itself. The route by which they may have reached these countries is easily
marked out. Immediately south of Cape Horn, at a distance of only 500
miles, are the South Shetland Islands and Graham's Land, whence the
Antarctic continent or a {522} group of large islands probably extends
across or around the south polar area to Victoria Land and thence to Adelie
Land. The outlying Young Island, 12,000 feet high, is about 750 miles south
of the Macquarie Islands, which may be considered a southern outlier of the
New Zealand group; and the Macquarie Islands are about the same distance
from the 1,000-fathom line at a point marking the probable southern
extension of Tasmania. Other islands may have existed at intermediate
points; but, even as it is, these distances are not greater than we know
are traversed by plants both by flotation and by aerial currents,
especially in such a stormy atmosphere as that of the Antarctic regions.
Now, we may further assume, that what we know occurred within the Arctic
circle also took place in the Antarctic--that is, that there have been
alternations of climate during which some portion of what are now ice-clad
lands became able to support a considerable amount of vegetation.[142]
During such periods there would be a steady migration of plants from all
southern circumpolar countries to people the comparatively unoccupied
continent, and the southern extremity of America being considerably the
nearest, and also being the best stocked with those northern types which
have such great powers of migration and colonisation, such plants would
form the bulk of the Antarctic vegetation, and during the continuance of
the milder southern climate would occupy the whole area.
When the cold returned and the land again became ice-clad, these plants
would be crowded towards the outer margins of the Antarctic land and its
islands, and some of them would find their way across the sea to such
countries as offered on their mountain summits suitable cool stations; and
as this process of alternately receiving plants from Chile and Fuegia and
transmitting them in all directions from the central Antarctic land may
have been {523} repeated several times during the Tertiary period, we have
no difficulty in understanding the general community between the European
and Antarctic plants found in all south temperate lands. Kerguelen's Land
and The Crozets are within about the same distance from the Antarctic
continent as New Zealand and Tasmania, and we need not therefore be
surprised at finding in each of these islands some Fuegian species which
have not reached the others. Of course, there will remain difficulties of
detail, as there always must remain, so long as our knowledge of the past
changes of the earth's surface and the history of the particular plants
concerned is so imperfect. Sir Joseph Hooker notes, for example, the
curious fact that several Compositae common to three such remote localities
as the Auckland Islands, Fuegia, and Kerguelen's Land, have no pappus or
seed-down, while such as have pappus are in no case common even to two of
these islands. Without knowing the exact history and distribution of the
genera to which these plants belong it would be useless to offer any
conjecture, except that they are ancient forms which may have survived
great geographical changes, or may have some peculiar and exceptional means
of dispersion.
_Proofs of Migration by way of the Himalayas and Southern Asia._--But
although we may thus explain the presence of a considerable portion of the
European element in the floras of New Zealand and Australia, we cannot
account for the whole of it by this means, because Australia itself
contains a host of European and Asiatic genera of which we find no trace in
New Zealand or South America, or any other Antarctic land. We find, in
fact, in Australia two distinct sets of European plants. First we have a
number of species identical with those of Northern Europe or Asia (of the
most characteristic of which--thirty-eight in number--Sir Joseph Hooker
gives a list); and in the second place a series of European genera usually
of a somewhat more southern character, mostly represented by very distinct
species, and all absent from New Zealand; such as Clematis, Papaver,
Cleome, Polygala, Lavatera, Ajuga, &c. Now of the first set--the North
European _species_--about three-fourths occur in some parts of America,
{524} and about half in South Temperate America or New Zealand; whence we
may conclude that most of these, as well as some others, have reached
Australia by the route already indicated. The second set of
Australo-European genera, however, and many others characteristic of the
South European or the Himalayan flora, have probably reached Australia by
way of the mountains of Southern Asia, Borneo, the Moluccas, and New
Guinea, at a somewhat remote period when loftier ranges and some
intermediate peaks may have existed, sufficient to carry on the migration
by the aid of the alternate climatal changes which are known to have
occurred. The long belt of Secondary and Palaeozoic formations in East
Australia from Tasmania to Cape York continued by the lofty ranges of New
Guinea, indicates the route of this immigration, and sufficiently explains
how it is that these northern types are almost wholly confined to this part
of the Australian continent. Some of the earlier immigrants of this class
no doubt passed over to New Zealand and now form a portion of the peculiar
genera confined to these two countries; but most of them are of later date,
and have thus remained in Australia only.
_Proofs of Migration by way of the African Highlands._--It is owing to this
twofold current of vegetation flowing into Australia by widely different
routes that we have in this distant land a better representation of the
European flora, both as regards species and genera, than in any other part
of the southern hemisphere; and, so far as I can judge of the facts, there
is no general phenomenon--that is, nothing in the distribution of genera
and other groups of plants as opposed to cases of individual species--that
is not fairly accounted for by such an origin. It further receives support
from the case of South Africa, which also contains a large and important
representation of the northern flora. But here we see no indications (or
very slight ones) of that southern influx which has given Australia such a
community of vegetation with the Antarctic lands. There are no less than
sixty _genera_ of strictly north temperate plants in South Africa, none of
which occur in Australia; while very few of the _species_, so
characteristic of Australia, New Zealand, and Fuegia, are found there. It
{525} is clear, therefore, that South Africa has received its European
plants by the direct route through the Abyssinian highlands and the lofty
equatorial mountains, and mostly at a distant period when the conditions
for migration were somewhat more favourable than they are now. The much
greater directness of the route from Northern Europe to South Africa than
to Australia; and the existence even now of lofty mountains and extensive
highlands for a large portion of the distance, will explain (what Sir
Joseph Hooker notes as "a very curious fact") why South Africa has more
very northern European _genera_ than Australia, while Australia has more
identical _species_ and a better representation on the whole of the
European flora--this being clearly due to the large influx of species it
has received from the Antarctic Islands, in addition to those which have
entered it by way of Asia. The greater distance of South Africa even now
from any of these islands, and the much deeper sea to the south of the
African continent, than in the case of Tasmania and New Zealand, indicating
a smaller recent extension southward, is all quite in harmony with the
facts of distribution of the northern flora above referred to.
_Supposed Connection of South Africa and Australia._--There remains,
however, the small amount of direct affinity between the vegetation of
South Africa and that of Australia, New Zealand, and Temperate South
America, consisting in all of fifteen genera, five of which are confined to
Australia and South Africa, while several natural orders are better
represented in these two countries than in any other part of the world.
This resemblance has been supposed to imply some former land-connection of
all the great southern lands, but it appears to me that any such
supposition is wholly unnecessary. The differences between the faunas and
floras of these countries are too great and too radical to render it
possible that any such connection should have existed except at a very
remote period. But if we have to go back so far for an explanation, a much
simpler one presents itself, and one more in accordance with what we have
learnt of the general permanence of deep oceans and the great changes that
have taken place {526} in the distribution of all forms of life. Just as we
explain the presence of marsupials in Australia and America and of
Centetidae in Madagascar and the Antilles, by the preservation in these
localities of remnants of once wide-spread types, so we should prefer to
consider the few genera common to Australia and South Africa as remnants of
an ancient vegetation, once spread over the northern hemisphere, driven
southward by the pressure of more specialised types, and now finding a
refuge in these two widely separated southern lands. It is suggestive of
such an explanation that these genera are either of very ancient groups--as
Conifers and Cycads--or plants of low organisation as the Restiaceae--or of
world-wide distribution, as Melanthaceae.
_The Endemic Genera of Plants in New Zealand._--Returning now to the New
Zealand flora, with which we are more especially concerned, there only
remains to be considered the peculiar or endemic genera which characterise
it. These are thirty-two in number, and are mostly very isolated. A few
have affinities with Arctic groups, others with Himalayan, or Australian
genera; several are tropical forms, but the majority appear to be
altogether peculiar types of world-wide groups--as Leguminosae,
Saxifrageae, Compositae, Orchideae, &c. We must evidently trace back these
peculiar forms to the earliest immigrants, either from the north or from
the south; and the great antiquity we are obliged to give to New
Zealand--an antiquity supported by every feature in its fauna and flora, no
less than by its geological structure, and its extinct forms of
life[143]--affords ample time for the changes in the general distribution
of plants, and for those due to isolation and modification under {527} the
influence of changed conditions, which are manifested by the extreme
peculiarity of many of these interesting endemic forms.
_The Absence of Southern Types from the Northern Hemisphere._--We have now
only to notice the singular want of reciprocity in the migrations of
northern and southern types of vegetation. In return for the vast number of
European plants which have reached Australia, not one single Australian
plant has entered any part of the north temperate zone, and the same may be
said of the typical southern vegetation in general, whether developed in
the Antarctic lands, New Zealand, South America, or South Africa. The
furthest northern outliers of the southern flora are a few genera of
Antarctic type on the Bornean Alps; the genus Acaena which has a species in
California; two representatives of the Australian flora--Casuarina and
Stylidium, in the peninsula of India; while China and the Philippines have
two strictly Australian genera of Orchideae--Microtis and Thelymitra, as
well as a Restiaceous genus. Several distinct causes appear to have
combined to produce this curious inability of the southern flora to make
its way into the northern hemisphere. The primary cause is, no doubt, the
totally different distribution of land in the two hemispheres, so that in
the south there is the minimum of land in the colder parts of the temperate
zone and in the north the maximum. This is well shown by the fact that on
the parallel of Lat. 50deg N. we pass over 240deg of land or shallow sea,
while on the same parallel of south latitude we have only 4deg, where we
cross the southern part of Patagonia. Again the three most important south
temperate land-areas--South Temperate America, South Africa, and
Australia--are widely separated from each other, and have in all
probability always been so; whereas the whole of the north temperate lands
are practically continuous. It follows that, instead of the enormous
northern area, in which highly organised and dominant groups of plants have
been developed gifted with great colonising and aggressive powers, we have
in the south three comparatively small and detached areas, in which rich
floras have been developed with _special_ {528} adaptations to soil,
climate, and organic environment, but comparatively impotent and inferior
beyond their own domain.
Another circumstance which makes the contest between the northern and
southern forms still more unequal, is the much greater hardiness of the
former, from having been developed in a colder region, and one where alpine
and arctic conditions extensively prevail; whereas the southern floras have
been mainly developed in mild regions to which they have been altogether
confined. While the northern plants have been driven north or south by each
succeeding change of climate, the southern species have undergone
comparatively slight changes of this nature, owing to the areas they occupy
being unconnected with the ice-bearing Antarctic continent. It follows,
that whereas the northern plants find in all these southern lands a milder
and more equable climate than that to which they have been accustomed, and
are thus often able to grow and flourish even more vigorously than in their
native land, the southern plants would find in almost every part of Europe,
North America or Northern Asia, a more severe and less equable climate,
with winters that usually prove fatal to them even under cultivation. These
causes, taken separately, are very powerful, but when combined they must, I
think, be held to be amply sufficient to explain why examples of the
typical southern vegetation are almost unknown in the north temperate zone,
while a very few of them have extended so far as the northern tropic.[144]
{529}
_Concluding Remarks on the Last Two Chapters._--Our inquiry into the
external relations and probable origin of the fauna and flora of New
Zealand, has thus led us on to a general theory as to the cause of the
peculiar biological relations between the northern and the southern
hemispheres; and no better or more typical example could be found of the
wide range and great interest of the study of the geographical distribution
of animals and plants.
The solution which has here been given of one of the most difficult of this
class of problems, has been rendered possible solely by the knowledge very
recently obtained of the form of the sea-bottom in the southern ocean, and
of the geological structure of the great Australian continent. Without this
knowledge we should have nothing but a series of guesses or probabilities
on which to found our hypothetical explanation, which we have now been able
to build up on a solid foundation of fact. The complete separation of East
from West Australia during a portion of the Cretaceous and Tertiary
periods, could never have been guessed till it was established by the
laborious explorations of the Australian geologists; while the hypothesis
of a comparatively shallow sea, uniting New Zealand by a long route with
tropical Australia, while a profoundly deep ocean always separated it from
temperate Australia, would have been rejected as too improbable a
supposition for the foundation of even the most enticing theory. Yet it is
mainly by means of these two facts, that we are enabled to give an adequate
explanation of the strange anomalies in the flora of Australia and its
relation to that of New Zealand.
In the more general explanation of the relations of the various northern
and southern floras, I have shown what an important aid to any such
explanation is the theory of repeated changes of climate, not necessarily
of great amount, given in Chapters VIII. and IX.; while the whole
discussion justifies the importance attached to the theory of the general
permanence of continents and oceans, as demonstrated in Chapter VI., since
any rational explanation based upon facts (as opposed to mere unsupported
{530} conjecture) must take such general permanence as a starting-point.
The whole inquiry into the phenomena presented by islands, which forms the
main subject of the present volume has, I think, shown that this theory
does afford a firm foundation for the discussion of questions of
distribution and dispersal; and that by its aid, combined with a clear
perception of the wonderful powers of dispersion and modification in the
organic world when long periods are considered, the most difficult problems
connected with this subject cease to be insoluble.
* * * * *
{531}
CHAPTER XXIV
SUMMARY AND CONCLUSION
The Present Volume is the Development and Application of a
Theory--Statement of the Biological and Physical Causes of
Dispersal--Investigation of the Facts of Dispersal--of the Means of
Dispersal--of Geographical Changes Affecting Dispersal--of Climatal
Changes Affecting Dispersal--The Glacial Epoch and its Causes--Alleged
Ancient Glacial Epochs--Warm Polar Climates and their
Causes--Conclusions as to Geological Climates--How far Different from
those of Mr. Croll--Supposed Limitations of Geological Time--Time Amply
Sufficient both for Geological and Biological Development--Insular
Faunas and Floras--The North Atlantic Islands--The Galapagos--St.
Helena and the Sandwich Islands--Great Britain as a Recent Continental
Island--Borneo and Java--Japan and Formosa--Madagascar as an Ancient
Continental Island--Celebes and New Zealand as Anomalous Islands--The
Flora of New Zealand and its Origin--The European Element in the South
Temperate Floras--Concluding Remarks.
The present volume has gone over a very wide field both of facts and
theories, and it will be well to recall these to the reader's attention and
point out their connection with each other, in a concluding chapter. I hope
to be able to show that, although at first sight somewhat fragmentary and
disconnected, this work is really the development of a clear and definite
theory, and its application to the solution of a number of biological
problems. That theory is, briefly, that the distribution of the various
species and groups of living things over the earth's surface, and their
aggregation in definite assemblages in certain areas, is the {532} direct
result and outcome of a complex set of causes, which may be grouped as
"biological" and "physical." The biological causes are mainly of two
kinds--firstly, the constant tendency of all organisms to increase in
numbers and to occupy a wider area, and their various powers of dispersion
and migration through which, when unchecked, they are enabled to spread
widely over the globe; and, secondly, those laws of evolution and
extinction which determine the manner in which groups of organisms arise
and grow, reach their maximum, and then dwindle away, often breaking up
into separate portions which long survive in very remote regions. The
physical causes are also mainly of two kinds. We have, first, the
geographical changes which at one time isolate a whole fauna and flora, at
another time lead to their dispersal and intermixture with adjacent faunas
and floras--and it was here important to ascertain and define the exact
nature and extent of these changes, and to determine the question of the
general stability or instability of continents and oceans; in the second
place, it was necessary to determine the exact nature, extent and frequency
of the changes of climate which have occurred in various parts of the
earth,--because such changes are among the most powerful agents in causing
the dispersal and extinction of plants and animals. Hence the importance
attached to the question of geological climates and their causes, which
have been here investigated at some length with the aid of the most recent
researches of geologists, physicists, and explorers. These various
inquiries led on to an investigation of the mode of formation of stratified
deposits, with a view to fix within some limits their probable age; and
also to an estimate of the probable rate of development of the organic
world; and both these processes are shown to involve, so far as we can
judge, periods of time less vast than have generally been thought
necessary.
The numerous facts and theories established in the First Part of the work
are then applied to explain the phenomena presented by the floras and
faunas of the chief islands of the globe, which are classified, in
accordance with their physical origin, in three groups or classes, each
{533} of which are shown to exhibit certain well-marked biological
features.