_eleventh_ chapter. Mr. Miller shows, in the clearest manner, that
“superposition is not parental relation,” or that an organism lying
above another gives us no ground for believing that the lower organism
was the parent of the higher. The theorist, however, looks only at those
phases of truth which are in unison with his own views; and, when truth
presents no such favorable aspect, he finally wraps himself up in the
folds of ignorance and ambiguity—the winding-sheet of error refuted
and exposed. We have not yet penetrated, says he, in feeble accents,
to the formations which represent the dawn of being, and the simplest
organism may yet be detected beneath the lowest fossiliferous rocks.
This undoubtedly _may be_, and Sir Charles Lyell and Mr. Leonard Horner
are of opinion that such rocks may yet be discovered; while Sir Roderick
Murchison and Professor Sedgwick and Mr. Miller are of an opposite
opinion. But even were such rocks discovered to-morrow, it would not
follow that their organisms gave the least support to the development
hypothesis. In the year 1837, when fishes were not discovered in the
Upper Silurian rocks, the theorist would have rightly predicted the
existence of lower fossiliferous beds; but when they are discovered, and
their fossils examined, they furnish the strongest argument that could
be desired against the theory they were expected to sustain. This fact,
no doubt, is so far in favor of the supposition that there may be still
lower fossil-bearing strata; but, as Mr. Miller observes, “The pyramid of
organized existence, as it ascends into the by-past eternity, inclines
sensibly towards its apex,—that apex of ‘_beginning_’ on which, on far
other than geological grounds, it is our privilege to believe. The broad
base of the superstructure planted on the existing scene stretches across
the entire scale on life, animal and vegetable; but it contracts as it
rises into the past;—man,—the quadrumana,—the quadrupedal man,—the bird
and the reptile are each in succession struck from off its breadth, till
we at length see it with the vertebrata, represented by only the fish,
narrowing as it were to a point; and though the clouds of the upper
region may hide its apex, we infer, from the declination of its sides,
that it cannot penetrate much farther into the profound.”
In our author’s next chapter, the _twelfth_ of the series, he proceeds
to examine the “Lamarckian hypothesis of the origin of plants, and its
consequences.”
In his _thirteenth_ chapter, on “The two Floras, marine and terrestrial,”
he has shown that all our experience is opposed to the opinion, that the
one has been transmuted into the other. If the marine had been converted
into terrestrial vegetation, we ought to have, in the Lake of Stennis,
for example, plants of an intermediate character between the algæ of the
sea, and the monocotyledons of the lake. But no such transition-plants
are found. The algæ, as our author observes, become dwarfish and
ill-developed. They cease to exist as the water becomes fresher, “until
at length we find, instead of the brown, rootless, flowerless fucoids and
confervæ of the ocean, the green, rooted, flowering flags, rushes, and
aquatic grasses of the fresh water. Many thousands of years have failed
to originate a single intermediate plant.” The same conclusion may be
drawn from the character of the vegetation along the extensive shores of
Britain and Ireland. No botanist has ever found a single plant in the
transition state.
The _fourteenth_ chapter of the “Footprints” will be perused with great
interest by the general reader. It is a powerful and argumentative
exposure of the development hypothesis, and of the manner in which the
subject has been treated in the “Vestiges.” Whether we consider it in
its nature, in its history, or in the character of the intellects with
whom it originated, or by whom it has been received and supported, Mr.
Miller has shown that it has nothing to recommend it. It existed as a
wild dream before Geology had any being as a science. It was broached
more than a century ago by De Maillet, who knew nothing of the geology
even of his day. In a translation of his Telhamed, published in 1750,
Mr. Miller finds very nearly the same account given of the origin of
plants and animals, as that in the “Vestiges,” and in which the sea
is described as that “great and fruitful womb of nature, in which
organization and life first begin.” Lamarck, though a skilful botanist
and conchologist, was unacquainted with geology; and as he first
published his development hypothesis in 1802, (an hypothesis identical
with that of the “Vestiges,”) it is probable that he was not then a very
skilful zoologist. Nor has Professor Oken any higher claims to geological
acquirements. He confesses that he wrote the first edition of his work
in _a kind of inspiration!_ and it is not difficult to estimate the
intelligence of the inspiring idol that announced to the German sage that
the globe was a vast crystal, a little flawed in the facets, and that
quartz, feldspar, and mica, the three constituents of granite, were the
hail-drops of heavy showers of stone that fell into the original ocean,
and accumulated into rocks at the bottom!
Such is the unscientific parentage of the theories promulgated in the
“Vestiges.” But the author of this work appeals in the first instance to
science. Astronomy, Geology, Botany, and Zoology are called upon to give
evidence in his favor; but the astronomer, geologist, botanist, and the
zoologist, all refuse him their testimony, deny his premises, and reject
his results. “It is not,” as Mr. Miller happily observes, “the illiberal
religionist that casts him off. It is the inductive philosopher.” Science
addresses him in the language of the possessed: “The astronomer I know,
and the geologist I know; but who are ye?” Thus left alone in a cloud
of star-dust, or in brackish water between the marine and terrestrial
flora, he “appeals from science to the want of it,” casts a stone at
our Scientific Institutions, and demands a jury of “ordinary readers,”
as the only “tribunal” by which “the new philosophy is to be truly and
righteously judged.”
The last and _fifteenth_ chapter of Mr. Miller’s work, “On the Bearing
of Final Causes on Geologic History,” if read with care and thought,
will prove at once delightful and instructive. The principle of _final
causes_, or the conditions of existence, affords a wide scope to our
reason in Natural History, but especially in Geology. It becomes an
interesting inquiry, if any reason can be assigned why at certain periods
species began to exist, and became extinct after the lapse of lengthened
periods of time, and why the higher classes of being succeeded the lower
in the order of creation? The incompleteness of geological science,
however, does not permit us to remove, for the present, the veil which
hangs over this mysterious chronology; but our author is of opinion that
in about a quarter of a century, in a favored locality like the British
Islands, geological history “will assume a very extraordinary form.”
It is a singular fact, which will yet lead to singular results, that
Cuvier’s arrangement of the four classes of vertebrate animals should
exhibit the same order as that in which they are found in the strata of
the earth. In the _fish_, the average proportion of the brain to the
spinal cord is only as 2 to 1. In the _reptile_, the ratio is 2½ to 1.
In the _bird_, it is as 3 to 1. In the _mammalia_, it is as 4 to 1; and
in _man_, it is as 23 to 1. No less remarkable is the fœtal progress of
the human brain. It first becomes a brain resembling that of a fish; then
it grows into the form of that of a reptile; then into that of a bird;
then into that of a mammiferous quadruped, and finally it assumes the
form of a human brain, “thus comprising in its fœtal progress an epitome
of geological history, as if man were in himself a compendium of all
animated nature, and of kin to every creature that lives.”
With these considerations, Mr. Miller has brought his subject to the
point at which Science in its onward progress now stands. It is to
embryology we are in future to look for further information upon the
most intimate relations which exist between all organized beings. We may
fairly entertain the hope that the time is not far when we shall not
only fully understand the Plan of Creation, but even lift some corner
of the veil which has hitherto prevented us from forming adequate ideas
of the first introduction of animal and vegetable life upon earth, and
of the changes which both kingdoms have undergone in the succession of
geological ages.
L. AGASSIZ.
CAMBRIDGE, _September, 1850_.
CONTENTS
PAGE
STROMNESS AND ITS ASTEROLEPIS.—THE LAKE OF STENNIS 21
THE DEVELOPMENT HYPOTHESIS, AND ITS CONSEQUENCES 37
THE RECENT HISTORY OF THE ASTEROLEPIS.—ITS FAMILY 48
CEREBRAL DEVELOPMENT OF THE EARLIER VERTEBRATA.—ITS
APPARENT PRINCIPLE 62
THE ASTEROLEPIS.—ITS STRUCTURE, BULK, AND ASPECT 94
FISHES OF THE SILURIAN ROCKS, UPPER AND LOWER.—THEIR RECENT
HISTORY, ORDER, AND SIZE 130
HIGH STANDING OF THE PLACOIDS.—OBJECTIONS CONSIDERED 147
THE PLACOID BRAIN.—EMBRYONIC CHARACTERISTICS NOT NECESSARILY
OF A LOW ORDER 160
THE PROGRESS OF DEGRADATION.—ITS HISTORY 181
EVIDENCE OF THE SILURIAN MOLLUSCS.—OF THE FOSSIL FLORA.—ANCIENT
TREE 205
SUPERPOSITION NOT PARENTAL RELATION.—THE BEGINNINGS OF LIFE 230
LAMARCKIAN HYPOTHESIS OF THE ORIGIN OF PLANTS.—ITS CONSEQUENCES 243
THE TWO FLORAS, MARINE AND TERRESTRIAL.—BEARING OF THE
EXPERIENCE ARGUMENT 262
THE DEVELOPMENT HYPOTHESIS IN ITS EMBRYONIC STATE.—OLDER THAN
ITS ALLEGED FOUNDATIONS 277
FINAL CAUSES—THEIR BEARING ON GEOLOGIC HISTORY—CONCLUSION 303
LIST OF WOOD-CUTS
PAGE
1. Internal ridge of hyoid plate of _Asterolepis_ 31
2. Shagreen of _Raja clavata_:—of _Sphagodus_ 54
3. Scales of _Acanthodes sulcatus_:—shagreen of _Scyllium
stellare_ 55
4. Scales of _Cheiracanthus microlepidotus_:—shagreen of
_Spinax Acanthias_ 56
5. Section of shagreen of _Scyllium stellare_:—of scales of
_Cheiracanthus microlepidotus_ 56
6. Scales of _Osteolepis microlepidotus_:—of an undescribed
species of _Glyptolepis_ 57
7. Osseous points Of Placoid Cranium 65
8. Osseous centrum of _Spinax Acanthias_:—of _Raja clavata_ 67
9. Portions of caudal fin of _Cheiracanthus_:—of _Cheirolepis_ 69
10. Upper surface of cranium of Cod 72
11. Cranial buckler of _Coccosteus_ 74
12. Cranial buckler of _Osteolepis_ 75
13. Upper surface of head of _Osteolepis_ 77
14. Under surface of head of _Osteolepis_ 79
15. Head of _Osteolepis_, seen in profile 80
16. Cranial buckler of _Diplopterus_ 81
17. Ditto 82
18. Palatal dart-head, and group of palatal teeth, of _Dipterus_ 83
19. Cranial buckler of _Dipterus_ 85
20. Base of cranium of _Dipterus_ 86
21. Under jaw of _Dipterus_ 87
22. Longitudinal section of head of _Dipterus_ 88
23. Section of vertebral centrum of Thornback 92
24. Dermal tubercles of _Asterolepis_ 95
25. Scales of _Asterolepis_ 96
26. Portion of carved surface of scale 96
27. Cranial buckler of _Asterolepis_ 98
28. Inner surface of cranial buckler of _Asterolepis_ 99
29. Plates of cranial buckler of _Asterolepis_ 102
30. Portion of under jaw of _Asterolepis_ 103
31. Inner side of portion of under jaw of _Asterolepis_ 104
32. Portion of transverse section of reptile tooth of
_Asterolepis_ 105
33. Section of jaw of _Asterolepis_ 106
34. Maxillary bone? 108
35. Inner surface of operculum of _Asterolepis_ 109
36. Hyoid plate 110
37. Nail-like bone of hyoid plate 111
38. Shoulder plate of _Asterolepis_ 112
39. Dermal bones of _Asterolepis_ 113
40. Internal bones of _Asterolepis_ 114
41. Ditto 115
42. Ischium of _Asterolepis_ 116
43. Joint of ray of Thornback:—of _Asterolepis_ 117
44. Coprolites of _Asterolepis_ 118
45. Hyoid plate of Thurso _Asterolepis_ 124
46. Hyoid plate of Russian _Asterolepis_ 127
47. Spine of _Spinax Acanthias_:—fragment of Onondago spine 143
48. Tail of _Spinax Acanthius_:—of _Ichthyosaurus tenuirostris_ 172
49. Port Jackson Shark (_Cestracion Phillippi_) 177
50. Tail of _Osteolepis_ 195
51. Tail of _Lepidosteus osseus_ 196
52. Tail of Perch 197
53. _Altingia excelsa_ (Norfolk-Island Pine) 212
54. Fucoids of the Lower Old Red Sandstone 216
55. Two species of Old Red Fucoids 217
56. Fern (?) of the Lower Old Red Sandstone 219
57. Lignite of the Lower Old Red Sandstone 221
58. Internal structure of lignite of Lower Old Red Sandstone 223
STROMNESS AND ITS ASTEROLEPIS. THE LAKE OF STENNIS.
When engaged in prosecuting the self-imposed task of examining in detail
the various fossiliferous deposits of Scotland, in the hope of ultimately
acquainting myself with them all, I extended my exploratory ramble, about
two years ago, into the Mainland of Orkney, and resided for some time in
the vicinity of Stromness.
This busy seaport town forms that special centre, in this northern
archipelago, from which the structure of the entire group can be most
advantageously studied. The geology of the Orkneys, like that of
Caithness, owes its chief interest to the immense development which
it exhibits of one formation,—the Lower Old Red Sandstone,—and to the
extraordinary abundance of its vertebrate remains. It is not too much
to affirm, that in the comparatively small portion which this cluster
of islands contains of the _third_ part of a system regarded only a
few years ago as the least fossiliferous in the geologic scale, there
are more fossil fish enclosed than in _every_ other geologic system
in England, Scotland, and Wales, from the Coal Measures to the Chalk
inclusive. Orkney is emphatically, to the geologist, what a juvenile
Shetland poetess designates her country, in challenging for it a standing
independent of the “Land of Cakes,”—a “Land of Fish;” and, were the trade
once fairly opened up, could supply with ichthyolites, by the ton and the
ship-load, the museums of the world. Its various deposits, with all their
strange organisms, have been uptilted from the bottom against a granitic
axis, rather more than six miles in length by about a mile in breadth,
which forms the great back-bone of the western district of Pomona; and on
this granitic axis—fast jammed in between a steep hill and the sea—stands
the town of Stromness. Situated thus _at the bottom_ of the upturned
deposits of the island, it occupies exactly such a point of observation
as that which the curious eastern traveller would select, in front of
some huge pyramid or hieroglyphic-covered obelisk, as a proper site for
his tent. It presents, besides, not a few facilities for studying with
the geological phenomena, various interesting points in physical science
of a cognate character. Resting on its granitic base, _in front_ of
the strangely sculptured pyramid of three broad tiers,—red, black, and
gray,—which the Old Red Sandstone of these islands may be regarded as
forming, it is but a short half mile from the Great Conglomerate base
of the formation, and scarcely a quarter of a mile more from the older
beds of its central flagstone deposit; while an hour’s sail on the one
hand opens to the explorer the overlying arenaceous deposit of Hoy, and
an hour’s walk on the other introduces him to the Loch of Stennis, with
its curiously mixed flora and fauna. But of the Loch of Stennis and its
productions more anon.
The day was far spent when I reached Stromness: but as I had a fine
bright evening still before me, longer by some three or four degrees of
north latitude than the midsummer evenings of the south of Scotland,
I set out, hammer in hand, to examine the junction of the granite and
the Great Conglomerate, where it has been laid bare by the sea along
the low promontory which forms the western boundary of the harbor. The
granite here is a ternary of the usual components, somewhat intermediate
in grain and color between the granites of Peterhead and Aberdeen;
and the conglomerate consists of materials almost exclusively derived
from it,—evidence enough of itself, that when this ancient mechanical
deposit was in course of forming, the granite—exactly such a compound
then as it is now—was one of the surface rocks of the locality, and
much exposed to disintegrating influences. This conglomerate base of
the Lower Old Red Sandstone of Scotland—which presents, over an area
of many thousand square miles, such an identity of character, that
specimens taken from the neighborhood of Lerwick, in Shetland, or of
Gamrie, in Banff, can scarce be distinguished from specimens detached
from the hills which rise over the Great Caledonian Valley, or from the
cliffs immediately in front of the village of Contin—seems to have been
formed in a vast oceanic basin of primary rock,—a Palæozoic Hudson’s or
Baffin’s Bay,—partially surrounded, mayhap, by primary continents, swept
by numerous streams, rapid and headlong, and charged with the broken
debris of the inhospitable regions which they drained. The graptolite
bearing grauwacke of Banffshire seems to have been the only fossiliferous
rock that occurred throughout the entire extent of this ancient northern
basin; and its few organisms now serve to open the sole vista through
which the geological explorer to the north of the Grampians can catch a
glimpse of an earlier period of existence than that represented by the
ichthyolites of the Lower Old Red Sandstone.
Very many ages must have passed ere, amid waves and currents, the
water-worn debris which now forms the Great Conglomerate could have
accumulated over tracts of sea-bottom from ten to fifteen thousand
square miles in area, to its present depth of from one to four hundred
feet. At length, however, a thorough change took place; but we can only
doubtfully speculate regarding its nature or cause. The bottom of the
Palæozoic basin became greatly less exposed. Some protecting circle of
coast had been thrown up around it; or, what is perhaps more probable,
it had sunk to a profounder depth, and the ancient shores and streams
had receded, through the depression, to much greater distances. And, in
consequence, the deposition of rough sand and rolled pebbles was followed
by a deposition of mud. Myriads of fish, of forms the most ancient
and obsolete, congregated on its banks or sheltered in its hollows;
generation succeeded generation, millions and tens of millions perished
mysteriously by sudden death; shoals after shoals were annihilated; but
the productive powers of nature were strong, and the waste was kept
up. But who among men shall reckon the years or centuries during which
these races existed, and this muddy ocean of the remote past spread out
to unknown and nameless shores around them? As in those great cities of
the desert that lie uninhabited and waste, we can but conjecture their
term of existence from the vast extent of their cemeteries. We only
know that the dark, finely-grained schists in which they so abundantly
occur must have been of comparatively slow formation, and that yet the
thickness of the deposit more than equals the height of our loftiest
Scottish mountains. It would seem as if a period equal to that in which
all human history is comprised might be cut out of a corner of the period
represented by the Lower Old Red Sandstone, and be scarce missed when
away; for every year during which man has lived upon earth, it is not
improbable that the _Pterichthys_ and its contemporaries may have lived a
century. Their last hour, however, at length came. Over the dark-colored
ichthyolitic schists so immensely developed in Caithness and Orkney,
there occurs a pale-tinted, unfossiliferous sandstone, which in the
island of Hoy rises into hills of from fourteen to sixteen hundred feet
in height; and among the organisms of those newer formations of the Old
Red which overlie this deposit, not a species of ichthyolite identical
with the species entombed in the lower schists has yet been detected. In
the blank interval which the arenaceous deposit represents, tribes and
families perished and disappeared, leaving none of their race to succeed
them, that other tribes and families might be called into being, and fall
into their vacant places in the onward march of creation.
Such, so far as the various hieroglyphics of the pile have yet rendered
their meanings to the geologist, is the strange story recorded on the
three-barred _pyramid_ of Stromness. I traced the formation upwards this
evening along the edges of the upturned strata, from where the Great
Conglomerate leans against the granite, till where it merges into the
ichthyolitic flagstones; and then pursued these from older and lower to
newer and higher layers, desirous of ascertaining at what distance over
the base of the system its more ancient organisms first appear, and what
their character and kind. And, embedded in a grayish-colored layer of
hard flag, somewhat less than a hundred yards over the granite, and about
a hundred and sixty feet over the upper stratum of the conglomerate, I
found what I sought,—a well-marked bone,—in all probability the oldest
vertebrate remain yet discovered in Orkney. What, asks the reader, was
the character of this ancient organism of the Palæozoic basin?
As shown by its cancellated texture, palpable to the naked eye, and
still more unequivocally by the irregular complexity of fabric which
it exhibits under the microscope,—by its speck-like life-points or
canaliculi, that remind one of air-bubbles in ice,—its branching
channels, like minute veins, through which the blood must once have
flown,—and its general groundwork of irregular lines of corpuscular
fibre, that wind through the whole like currents in a river studded with
islands,—it was as truly osseous in its composition as the solid bones of
any of the reptiles of the Secondary, or the quadrupeds of the Tertiary
periods. And in form it closely resembled a large roofing-nail. With this
bone our more practised palæontologists are but little acquainted, for
no remains of the animal to which it belonged have yet been discovered
in Britain to the south of the Grampians,[3] nor, except in the Old Red
Sandstone of Russia, has it been detected any where on the Continent.
Nor am I aware that, save in the accompanying wood-cut, (fig. 1,) it has
ever been figured. The amateur geologists of Caithness and Orkney have,
however, learned to recognize it as the “petrified nail.” The length
of the entire specimen in this instance was five seven eighth inches,
the transverse breadth of the head two inches and a quarter, and the
thickness of the stem nearly three tenth parts of an inch. This nail-like
bone formed a characteristic portion of the _Asterolepis_,—so far as
is yet known, the most gigantic ganoid of the Old Red Sandstone, and,
judging from the _place_ of this fragment, apparently one of the first.
[Illustration: Fig. 1.
INTERNAL RIDGE OF HYOID PLATE OF ASTEROLEPSIS.[4]
(One third the natural size, linear.)]
There were various considerations which led me to regard the “petrified
nail” in this case as one of the most interesting fossils I had ever
seen; and, before quitting Orkney, to pursue my explorations farther to
the south, I brought two intelligent geologists of the district,[5] to
mark its place and character, that they might be able to point it out to
geological visitors in the future, or, if they preferred removing it to
their town museum, to indicate to them the stratum in which it had lain.
It showed me, among other things, how unsafe it is for the geologist to
base positive conclusions on merely negative data. Founding on the fact
that, of many hundred ichthyolites of the Lower Old Red Sandstone which
I had disinterred and examined, all were of comparatively small size,
while in the Upper Old Red many of the ichthyolites are of great mass and
bulk, I had inferred that vertebrate life had been restricted to minuter
forms at the commencement than at the close of the system. It had begun,
I had ventured to state in the earlier editions of a little work on the
“Old Red Sandstone,” with an age of dwarfs, and had ended with an age
of giants. And now, here, at the very base of the system, unaccompanied
by aught to establish the contemporary existence of its dwarfs,—which
appear, however, in an overlying bed about a hundred feet higher up,—was
there unequivocal proof of the existence of one of the most colossal of
its giants. But not unfrequently, in the geologic field, has the practice
of basing positive conclusions on merely negative grounds led to a
misreading of the record. From evidence of a kind exactly similar to that
on which I had built, it was inferred, some two or three years ago, that
there had lived no reptiles during the period of the Coal Measures, and
no fish in the times of the Lower Silurian System.