THE MESOZOIC AGES.
Physically, the transition from the Permian to the Trias is easy. In
the domain of life a great gulf lies between; and the geologist whose
mind is filled with the forms of the Palæozoic period, on rising into
the next succeeding beds, feels himself a sort of Rip Van Winkle, who
has slept a hundred years and awakes in a new world. The geography of
our continents seems indeed to have changed little from the time of
the Permian to that next succeeding group which all geologists
recognise as the beginning of the Mesozoic or Middle Age of the
world's history, the Triassic period. Where best developed, as in
Germany, it gives us the usual threefold series, conglomerates and
sandstones below, a shelly limestone in the middle, and sandstones and
marls above. Curiously enough, the Germans, recognising this
tripartite character here more distinctly then in their other
formations, named this the _Trias_ or triple group, a name which it
still retains, though as we have seen it is by no means the earliest
of the triple groups of strata. In England, where the middle limestone
is absent, it is a "New Red Sandstone," and the same name may be
appropriately extended to Eastern America, where bright red sandstones
are a characteristic feature. In the Trias, as in the Permian, the
continents of the northern hemisphere presented large land areas, and
there were lagoons and landlocked seas in which gypsum, magnesian
limestones, and rock salt were thrown down, a very eminent example of
which is afforded by the great salt deposits of Cheshire. There were
also tremendous outbursts of igneous activity along the margins of the
continents, more especially in Eastern America. But with all this
there was a rich land flora and a wonderful exuberance of new animal
life on the land; and in places there were even swamps in which pure
and valuable beds of coal, comparable with those of the old coal
formation, were deposited.
The triple division of the Trias as a cycle of the earth's history,
and its local imperfection, are well seen in the European development
of the group, thus:--
German Series. French Series. English Series.
Keuper, Sandstone and } Marnes Irisées {Saliferous and gypseous
Shale } { Shales and Sandstones.
Muschelkalk, Limestone} Calcaire Coquillier {Wanting.
and Dolomite }
Bunter, Sandstone and } Grès bigarré {Sandstone and
Conglomerate } { Conglomerate.
The Trias is succeeded by a great and complex system of formations,
usually known as the Jurassic, from its admirable development and
exposure in the range of the Jura; but which the English geologists
often name the "Oolitic," from the occurrence in it of beds of Oolite
or roe-stone. This rock, of which the beautiful cream-coloured
limestone of Bath is an illustration, consists of an infinity of
little spheres, like seeds or the roe of a fish. Under the microscope
these are seen to present concentric layers, each with a radiating
fibrous: structure, and often to have a minute grain of sand or
fragment of shell in the centre. They are, in short, miniature
concretions, produced by the aggregation of the calcareous matter
around centres, by a process of molecular attraction to which fine
sediments, and especially those containing much lime, are very prone.
This style of limestone is very abundant in the Jurassic system, but
it is not confined to it. I have seen very perfect Oolites in the
Silurian and the Carboniferous. The Jurassic series, as developed in
England, may be divided into three triplets or cycles of beds, in the
following way:
{Purbeck Beds.
Upper Jurassic {Portland Limestone.
{Portland Sand.
{Kimmeridge Clay, etc.
Middle Jurassic {Coral Rag, Limestone.
{Lower Calcareous Grit, Oxford Clay, etc.
{Cornbrash and Forest Marble.
Lower Jurassic[AD] {Great and inferior Oolite, Limestone.
{Lias Clays and Limestones.
[AD] This last group is very complex, and might perhaps admit of sub
division, locally at least, into subordinate cycles.
These rocks occupy a large space in England, as the names above given
will serve to show; and they are also largely distributed over the
continent of Europe and Asia which had evidently three great and
long-continued dips under water, indicated by the three great
limestones. In America the case was different. The Jurassic has not
been distinctly recognised in any part of the eastern coast of that
continent, which then perhaps extended farther into the Atlantic then
it does at present; so that no marine beds were formed on its eastern
border. But in the west, along the base of the Rocky Mountains and
also in the Arctic area, there were Jurassic seas of large extent,
swarming with characteristic animals. At the close of the Jurassic
period our continents seem to have been even more extensive then at
present. In England and the neighbouring parts of the continent of
Europe, according to Lyell, the fresh-water and estuarine beds known
as the Wealden have been traced 320 miles from west to east, and 200
miles from north-west to south-east, and their thickness in one part
of this area is estimated at no less then 2,000 feet. Such a deposit
is comparable in extent with the deltas of such great rivers as the
Niger or even the Mississippi, and implies the existence of a
continent much more extensive and more uniform in drainage then Europe
as it at present exists. Lyell even speculates on the possible
existence of an Atlantic continent west of Europe. America also at
this time had, as already stated, attained to even more then its
present extension eastwards. Thus this later Jurassic period was the
culmination of the Mesozoic, the period of its most perfect
continental development, corresponding in this to the Carboniferous in
the Palæozoic.
The next or closing period of this great Mesozoic time brought a
wondrous change. In the Cretaceous period, so called from the vast
deposits of chalk by which it is characterized, the continents sunk as
they had never sunk before, so that vast spaces of the great
continental plateaus were brought down, for the first time since the
Laurentian, to the condition of abyssal depths, tenanted by such
creatures as live in the deepest recesses of our modern oceans. This
great depression affected Europe more severely then America; the
depression of the latter being not only less, but somewhat later in
date. In Europe, at the period of greatest submergence, the hills of
Scandinavia and of Britain, and the Urals, perhaps alone stood out of
the sea. The Alps and their related mountains, and even the Himalayas,
were not yet born, for they have on their high summits deep-sea beds
of the Cretaceous and even of later date. In America, the Appalachians
and the old Laurentian ranges remained above water; but the Rocky
Mountains and the Andes were in great part submerged, and a great
Cretaceous sea extended from the Appalachians westward to the Pacific,
and southward to the Gulf of Mexico, opening probably to the North
into the Arctic Ocean.
This great depression must have been of very long continuance, since
in Western Europe it sufficed for the production of nearly 1,000 feet
in thickness of chalk, a rock which, being composed almost entirely of
microscopic shells, is, as we shall see in the sequel, necessarily of
extremely slow growth. If we regard the Cretaceous group as one of our
great ages or cycles, it seems to be incomplete. The sandstones and
clays known as the Greensand and Gault constitute its lower or
shallow-water member. The chalk is its middle or deep-sea member, but
the upper shallow-water member is missing, or only very locally and
imperfectly developed. And the oldest of the succeeding Tertiary
deposits, which indicate much less continuous marine conditions, rest
on the chalk, as if the great and deep sea of the Cretaceous age had
been suddenly upheaved into land. This abrupt termination of the last
cycle of the Mesozoic is obviously the reason of the otherwise
inexplicable fact that the prevalent life of the period ceases at the
top of the chalk, and is exchanged immediately and without any
transition for the very different fauna of the Tertiary. This further
accords with the fact that the Cretaceous subsidence ended in another
great crumpling of the crust, like that which distinguished the
Permian. By this the Mesozoic time was terminated and the Cainozoic
inaugurated; while the Rocky Mountains, the Andes, the Alps, and the
Himalayas, rose to importance as great mountain ranges, and the
continents were again braced up to retain a condition of comparative
equilibrium during that later period of the earth's chronology to
which we ourselves belong.
[Illustration: LIFE ON LAND IN THE MESOZOIC PERIOD.
In the foreground are a Pine, Cycads, and a Pandanus; also small
Mammals, an herbivorous Dinosaur, and a Labyrinthodont. In the
distance are other Dinosaurs and Crocodiles. In the air are birds
(_Archæopterux_) and Pterodactyls.
Was the length of the Mesozoic time equal to that of the Palæozoic?
Measured by recurring cycles it was. In the latter period we find five
great cycles, from the Lower Silurian to the Permian inclusive. So in
the Mesozoic we have five also, from the Trias to the Cretaceous
inclusive. We have a right to reckon these cycles as ages or great
years of the earth; and so reckoning them, the Mesozoic time may have
been as long as the Palæozoic. But if we take another criterion the
result will be different. The thickness of the deposits in the
Palæozoic as compared with the Mesozoic, where these are severally
best developed, may be estimated as at least four or five to one; so
that if we suppose the beds to have been formed with equal rapidity in
the two great periods, then the older of the two was between four and
five times as long as the latter, which would indeed be only a little
greater then one of the separate ages of the Palæozoic. Either,
therefore, the deposits took place with greater rapidity in the
Palæozoic, or that period was by much the longer of the two. This it
will be observed, is only another aspect of the great laws of
geological sequence referred to in our last paper.
Let us look into this question a little more minutely. If the several
pulsations of our continents depended upon any regularly recurring
astronomical or terrestrial change, then they must represent, at least
approximately, equal portions of time, and this, if proved, would
settle the question in favour of an equal duration of these two great
eras of the earth's history. But as we cannot yet prove this, we may
consider what light we can derive from the nature of the rocks
produced. These may be roughly classified as of two kinds: First, the
beds of sediment, sand, clay, etc., accumulated by the slow chemical
decay of rocks and the mechanical agency of water. Secondly, the beds
formed by accumulation of the harder and less perishable parts of
living beings, of which the limestones are the chief. With reference
to the first of these kinds of deposit, the action of the atmosphere
and rains on rocks in the earlier times might have been somewhat more
powerful if there was more carbonic acid in the atmosphere, that
substance being the most efficient agent in the chemical decay of
rocks. It might have been somewhat more powerful if there was a
greater rainfall. It must, on the other hand, have been lessened by
the apparently more equable temperature which then prevailed. These
differences might perhaps nearly balance one another. Then the rocks
of the older time were quite as intractable as those of the newer, and
they were probably neither so high nor so extensive. Further, the dips
and emergences of the great continental plateaus were equally numerous
in the two great periods, though they were probably, with the
exception of the latest one of each, more complete in the older
period. In so far, then, as deposition of sediment is concerned, these
considerations would scarcely lead us to infer that it was more rapid
in the Palæozoic. But the Palæozoic sediments may be estimated in the
aggregate at about 50,000 feet in thickness, while those of the
Mesozoic scarcely reach 8,000. We might, therefore, infer that the
Palæozoic period was perhaps five or six times as long as the
Mesozoic.
If we take the second class of rocks, the limestones, and suppose
these to have been accumulated by the slow growth of corals, shells,
etc., in the sea, we might, at first sight, suppose that Palæozoic
animals would not grow or accumulate limestone faster then their
Mesozoic successors. We must, however, consider here the probability
that the older oceans contained more lime in solution then those which
now exist, and that the equable temperature and extensive submerged
plateaus gave very favourable conditions for the lower animals of the
sea, so that it would perhaps be fair to allow a somewhat more rapid
rate of growth of limestone for the Palæozoic. Now the actual
proportions of limestone may be roughly stated at 13,000 feet in the
Palæozoic, and 3,000 feet in the Mesozoic, which would give a
proportion of about four and a quarter to one; and as a foot of
limestone may be supposed on the average to require five times as long
for its formation as a foot of sediment, this would give an even
greater absolute excess in favour of the Palæozoic on the evidence of
the limestones an excess probably far too great to be accounted for by
any more favourable conditions for the secretion of carbonate of lime
by marine animals.
The data for such calculations are very uncertain, and three elements
of additional uncertainty closely related to each other must also be
noticed. The first is the unknown length of the intervals in which no
deposition whatever may have been taking place over the areas open to
our investigation. The second is the varying amounts in which material
once deposited may have been swept away by water. The third is the
amount of difference that may have resulted from the progressive
change of the geographical features of our continents. These
uncertainties would all tend to diminish our estimate of the relative
length of the Mesozoic. Lastly, the changes that have taken place in
living beings, though a good measure of the lapse of time, cannot be
taken as a criterion here, since there is much reason to believe that
more rapid changes of physical conditions act as an inducing cause of
rapid changes of life.
On the whole, then, taking such facts as we have, and making large
deductions for the several causes tending to exaggerate our conception
of Palæozoic time, we can scarcely doubt that the Palæozoic may have
been three times as long as the Mesozoic. If so, the continental
pulsations, and the changes in animal and vegetable life, must have
gone on with accelerated rapidity in the later period,--a conclusion
to which we shall again have occasion to refer when we arrive at the
consideration of the Tertiary or Neozoic time, and the age of man, and
the probable duration of the order of things under which we live.
I have given this preliminary sketch of the whole Mesozoic time,
because we cannot here, as in the Palæozoic, take up each age
separately; and now we must try to picture to ourselves the life and
action of these ages. In doing so we may look at, first, the plant
life of this period; second, animal life on the land; and third,
animal life in the waters and in the ocean depths.
The Mesozoic shores were clothed with an abundant flora, which changed
considerably in its form during the lapse of this long time; but yet
it has a character of its own distinct from that of the previous
Palæozoic and the succeeding Tertiary. Perhaps no feature of this
period is more characteristic then the great abundance of those
singular plants, the cycads, which in the modern flora are placed near
to the pines, but in their appearance and habit more resemble palms,
and which in the modern world are chiefly found in the tropical and
warm temperate zones of Asia and America. No plants certainly of this
order occur in the Carboniferous, where their nearest allies are
perhaps some of the Sigillariæ; and in the modern time the cycads are
not so abundant, nor do they occur at all in climates where their
predecessors appear to have abounded. In the quarries of the island of
Portland, we have a remarkable evidence of this in beds with numerous
stems of cycads still _in situ_ in the soil in which they grew, and
associated with stumps of pines which seem to have flourished along
with them. In further illustration of this point, I may refer to the
fact that Carruthers, in a recent paper, catalogues twenty-five
British species belonging to eight genera--a fact which markedly
characterizes the British flora of the Mesozoic period. These plants
will therefore occupy a prominent place in our restoration of the
Mesozoic landscape, and we should give especial prominence to the
beautiful species _Williamsonia gigas_, discovered by the eminent
botanist whose name it bears, and restored in his paper on the plant
in the "Linnæan Transactions." These plants, with pines and gigantic
equisetums, prevailed greatly in the earlier Mesozoic flora, but as
the time wore on, various kinds of endogens, resembling the palms and
the screw-pines of the tropical islands, were introduced, and toward
its close some representatives of the exogens very like our ordinary
trees. Among these we find for the first time in our upward progress
in the history of the earth, species of our familiar oaks, figs, and
walnut, along with some trees now confined to Australia and the Cape
of Good Hope, as the banksias and "silver-trees," and their allies. In
America a large number of the genera of the modern trees are present,
and even some of those now peculiar to America, as the tulip-trees and
sweet-gums. These forests of the later Mesozoic must therefore have
been as gay with flowers and as beautiful in foliage as those of the
modern world, and there is evidence that they swarmed with insect
life. Further, the Mesozoic plants produced in some places beds of
coal comparable in value and thickness to those of the old coal
formation. Of this kind are the coal beds of Brora in Sutherlandshire,
those of Richmond in Virginia, and Deep River in N. Carolina, those of
Vancouver's Island, and a large part of those of China. To the same
age have been referred some at least of the coal beds of Australia and
India. So important are these beds in China, that had geology
originated in that country, the Mesozoic might have been our age of
coal.
If the forests of the Mesozoic present a great advance over those of
the Palæozoic, so do the animals of the land, which now embrace all
the great types of vertebrate life. Some of these creatures have left
strange evidence of their existence in their footprints on the sand
and clay, now cemented into beds of hard rock excavated by the
quarryman. If we had landed on some wide muddy Mesozoic shore, we
might have found it marked in all directions with animal footprints.
Some of these are shaped much like a human hand. The creature that
made this mark was a gigantic successor of the crocodilian newts or
labyrinthodonts of the Carboniferous, and this type seems to have
attained its maximum in this period, where one species, _Labyrinthodon
giganteus_, had great teeth three or four inches in length, and
presenting in their cross section the most complicated foldings of
enamel imaginable. But we may see on the shores still more remarkable
footprints. They indicate biped and three-toed animals of gigantic
size, with a stride perhaps six feet in length. Were they enormous
birds? If so, the birds of this age must have been giants which would
dwarf even our ostriches. But as we walk along the shore we see many
other impressions, some of them much smaller and different in form.
Some, again, very similar in other respects, have four toes; and, more
wonderful still, in tracing up some of the tracks, we find that here
and there the creature has put down on the ground a sort of
four-fingered hand, while some of these animals seem to have trailed
long tails behind them. What were these portentous creatures--bird,
beast, or reptile? The answer has been given to us by their bones, as
studied by Yon Meyer and Owen, and more recently by Huxley and Cope.
We thus have brought before us the _Dinosaurs_--the terrible
Saurians--of the Mesozoic age, the noblest of the Tanninim of old.
These creatures constitute numerous genera and species, some of
gigantic size, others comparatively small;--some harmless browsers on
plants, others terrible renders of living flesh; but all remarkable
for presenting a higher type of reptile organization then any now
existing, and approaching in some respects to the birds and in others
to the mammalia. Let us take one example of each of the principal
groups. And first marches before us the _Iguanodon_ or his relation
_Hadrosaurus_--a gigantic biped, twenty feet or more in height, with
enormous legs shaped like those of an ostrich, but of elephantine
thickness. It strides along, not by leaps like a kangaroo, but with
slow and stately tread, occasionally resting, and supporting itself on
the tripod formed by its hind limbs and a huge tail, like the inverted
trunk of a tree. The upper part of its body becomes small and slender,
and its head, of diminutive size and mild aspect, is furnished with
teeth for munching the leaves and fruits of trees, which it can easily
reach with its small fore-limbs, or hands, as it walks through the
woods. The outward appearance of these creatures we do not certainly
know. It is not likely that they had bony plates like crocodiles, but
they may have shone resplendent in horny scale armour of varied hues.
But another and more dreadful form rises before us. It is
_Megalosaurus_ or perhaps _Lælaps_. Here we have a creature of equally
gigantic size and biped habits; but it is much more agile, and runs
with great swiftness or advances by huge leaps, and its feet and hands
are armed with strong curved claws; while its mouth has a formidable
armature of sharp-edged and pointed teeth. It is a type of a group of
biped bird-like lizards, the most terrible and formidable of rapacious
animals that the earth has ever seen. Some of these creatures, in
their short deep jaws and heads, resembled the great carnivorous
mammals of modern times, while all in the structure of their limbs had
a strange and grotesque resemblance to the birds. Nearly all
naturalists regard them as reptiles; but in their circulation and
respiration they must have approached to the mammalia, and their
general habit of body recalls that of the kangaroos. They were no
doubt oviparous; and this, with their biped habit, seems to explain
the strong resemblance of their hind quarters to those of birds. Had
we seen the eagle-clawed Lælaps rushing on his prey; throwing his huge
bulk perhaps thirty feet through the air, and crushing to the earth
under his gigantic talons some feebler Hadrosaur, we should have
shudderingly preferred the companionship of modern wolves and tigers
to that of those savage and gigantic monsters of the Mesozoic.
We must not leave the great land-lizards of the reptilian age, without
some notice of that Goliath of the race which, by a singular misnomer,
has received the appellation of _Ceteosaurus_ or "Whale-Saurian." It
was first introduced to naturalists by the discovery of a few enormous
vertebrae in the English Oolite; and as these in size and form seemed
best to fit an aquatic creature, it was named in accordance with this
view. But subsequent discoveries have shown that, incredible though
this at first appeared, the animal had limbs fitted for walking on the
land. Professor Phillips has been most successful in collecting and
restoring the remains of Ceteosaurus, and devotes to its history a
long and interesting section of his "Geology of Oxford." The size of
the animal may be estimated, from the fact that its thigh-bone is
sixty-four inches long, and thick in proportion. From this and other
fragments of the skeleton, we learn that this huge monster must have
stood ten feet high when on all fours, and that its length, could not
have been less then fifty feet; perhaps much more. From a single
tooth, which has been found, it seems to have been herbivorous; and it
was probably a sort of reptilian Hippopotamus, living on the rich
herbage by the sides of streams and marshes, and perhaps sometimes
taking to the water, where the strokes of its powerful tail would
enable it to move more rapidly then on the land. In structure, it
seems to have been a composite creature, resembling in many points the
contemporary Dinosaurs; but in others, approaching to the crocodiles
and the lizards.
But the wonders of Mesozoic reptiles are not yet exhausted. While
noticing numerous crocodiles and lizard: like creatures, and several
kinds of tortoises, we are startled by what seems a flight of great
bats, wheeling and screaming overhead, pouncing on smaller creatures
of their own kind, as hawks seize sparrows and partridges, and perhaps
diving into the sea for fish. These were the Pterodactyles, the
reptile bats of the Mesozoic. They fly by means of a membrane
stretched on a monstrously enlarged little finger, while the other
fingers of the fore limb are left free to be used as hands or feet. To
move these wings, they had large breast-muscles like those of birds.
In their general structure, they were lizards, but no doubt of far
higher organization then any animals of this order now living; and in
accordance with this, the interior of their skull shows that they must
have had a brain comparable with that of birds, which, they rivalled
in energy and intelligence. Some of them were larger then the largest
modern birds of prey, others were like pigeons and snipes in size.
Specimens in the Cambridge Museum indicate one species twenty feet in
the expanse of its wings. Cope has recently described an equally
gigantic species from the Mesozoic of Western America, and fragments
of much larger species are said to exist.[AE] Imagine such a creature,
a flying dragon, with vast skinny wings, its body, perhaps, covered
with scales, both wings and feet armed with strong claws, and with
long jaws furnished with sharp teeth. Nothing can be conceived more
strange and frightful. Some of them had the hind limbs long, like
wading birds. Some had short, legs, adapted perhaps for perching. They
could probably fold up their wings, and walk on all fours. Their
skeleton, like that of birds, was very light, yet strong; and the
hollow bones have pores, which show that, as in birds, air could be
introduced into them from the lungs. This proves a circulation
resembling that of birds, and warm blood. Indeed, in many respects,
these creatures bridge over the space between the birds and the
reptiles. "That they lived," says Seeley, "exclusively upon land or in
the air is improbable, considering the circumstances under which their
remains are found. It is likely that they haunted the sea-shores; and
while sometimes rowing themselves over the water with their powerful
wings, used the wing membrane, as does the bat, to encloses the prey
and bring it to the mouth. The large Pterodactyles probably pursued a
more substantial prey then dragon-flies. Their teeth were well suited
for fish; but probably fowl and small mammal, and even fruits, made a
variety in their food. As the lord of the cliff, it may be supposed to
have taken toll of all animals that could be conquered with tooth and
nail. From its brain, it might be regarded as an intelligent animal.
The jaws present indications of having been sheathed with a horny
covering, and some species show a rugose anterior termination of the
snout, suggestive of fleshy lips like those of the bat, and which may
have been similarly used to stretch and clean the wing-membrane."
[AE] Seeley: "_Ornithosauria._"
Here, however, perched on the trees, we see true birds. At least they
have beaks, and are clothed with feathers. But they have very strange
wings, the feathers all secondaries, without any large quills, and
several fingers with claws at the angle of the wing, so that though
less useful as wings, they served the double purpose of wing and hand.
More strange still, the tail was long and flexible, like that of a
lizard, with the feathers arranged in rows along its sides. If the
lizards of this strange and uncertain time had wings like bats, the
birds had tails and hands like lizards. This was in short the special
age of reptiles, when animals of that class usurped the powers which
rightfully belonged to creatures yet in their nonage, the true birds
and mammals of our modern days, while the birds were compelled to
assume some reptilian traits.
Yet, strange to say, representatives of the higher creatures destined
to inherit the earth at a later date actually existed. Toward the
close of the Mesozoic we find birds approaching to those of our own
day, and almost at the beginning of the time there were small mammals,
remains of which are found both in the earlier and later formations of
the Mesozoic, but which never seem to have thriven; at least so far as
the introduction of large and important species is concerned.
Traversing the Mesozoic woods, we might see here and there little
hairy creatures, which would strike a naturalist as allies of the
modern bandicoots, kangaroo rats, and myrmecobius of Australia; and
closer study would confirm this impression, though showing differences
of detail. In their teeth, their size, and general form, and probably
in their pouched or marsupial reproduction, these animals were early
representatives of the smaller quadrupeds of the Austral continent,
creatures which are not only small but of low organisation in their
class.
One of these mammals, known to us only by its teeth, and well named
_Microlestes_, the "little thief" sneaks into existence, so to speak,
in the Trias of Europe, while another very similar, _Dromatherium_,
appears in rocks of similar age in America; and this is the small
beginning of the great class Mammalia, destined in its quadrupedal
forms to culminate in the elephants and their contemporaries in the
Tertiary period. Who that saw them trodden under foot lay the
reptile aristocracy of the Mesozoic could have divined their destiny?
But, notwithstanding the struggle for existence, the weakest does not
always "go to the wall." The weak things of this world are often
chosen to confound those that are mighty; and the little quadrupeds of
the Mesozoic are an allegory. They may typify the true, the good, and
the hopeful, mildly and humbly asserting themselves in the world that
now is, in the presence of the dragon monsters of pride and violence,
which in the days to come they will overthrow. Physically the Mesozoic
has passed away, but still exists morally in an age of evil reptiles,
whose end is as certain as that of the great Dinosaurs of the old
world.
The Mesozoic mammals are among the most interesting fossils known to
us. In a recent memoir by Professor Owen, thirty-three species are
indicated--all, or nearly all, Marsupial--all small--all closely
allied to modern Australian animals; some herbivorous, some probably
carnivorous. Owen informs us that these animals are not merely
marsupials, but marsupials of low grade, a point in which, however,
Huxley differs somewhat in opinion. They are at least not lower then
some that still exist, and not so low as those lowest of mammals in
Modern Australia, the duck-billed platypus and the echidna. Owen
further supposes that they were possibly the first mammals, and not
only the predecessors but the progenitors of the modern marsupials. If
so, we have the singular fact that they not only did not improve
throughout the vast Mesozoic time, but that they have been in the
progress of subsequent geological ages expelled out of the great
eastern continent, and, with the exception of the American opossums,
banished, like convicts, to Australia. Yet, notwithstanding their
multiplied travels and long experiences, they have made little
advance. It thus seems that the Mesozoic mammals were, from the
evolutionist point of view, a decided failure, and the work of
introducing mammals had to be done over again in the Tertiary; and
then, as we shall find, in a very different way. If nothing more,
however, the Mesozoic mammals were a mute prophecy of a better time, a
protest that the age of reptiles was an imperfect age, and that better
things were in store for the world. Moses seems to have been more
hopeful of them then Owen or even Huxley would have been. He says that
God "created" the great Tanninim, the Dinosaurs and their allies, but
only "made" the mammals of the following creative day; so that when
Microlestes and his companions quietly and unnoticed presented
themselves in the Mesozoic, they would appear in some way to have
obviated, in the case of the tertiary mammals, the necessity of a
repetition of the greater intervention implied in the word "create."
How that was effected none of us know; but, perhaps, we may know
hereafter.