THE MESOZOIC AGES (_continued_).
The waters of the Mesozoic period present features quite as remarkable
as the land. In our survey of their teeming multitudes, we indeed
scarcely know where to begin or whither to turn. Let us look first at
the higher or more noble inhabitants of the waters. And here, just as
in the case of the greater animals of the land, the Mesozoic was
emphatically an age of reptiles. In the modern world the highest
animals the sea are mammals, and these belong to three great and
somewhat diverse groups. The first is that of the seals and their
allies, the walruses, sea-lions, etc. The second is that of the whales
and dolphins and porpoises. The third is that of the manatees, or
dugongs. All these creatures breathe air, and bring forth their young
alive, and nourish them with milk. Yet they all live habitually or
constantly in the water. Between these aquatic mammals and the fishes,
we have some aquatic reptiles as the turtles, and a few sea-snakes and
sea-lizards, and crocodiles; but the number of these is comparatively
small, and in the more temperate latitudes there are scarcely any of
them.
All this was different in the Mesozoic. In so far as we know, there
were no representatives of the seals and whales and their allies, but
there were vast numbers of marine reptiles, and many of these of
gigantic size. Britain at present does not possess one large reptile,
and no marine reptile whatever. In the Mesozoic, in addition to the
great Dinosaurs and Pterodactyls of the land, it had at least fifty or
sixty species of aquatic reptiles, besides many turtles. Some of these
were comparable in size with our modern whales, and armed with
tremendous powers of destruction. America is not relatively rich in
remains of Mesozoic Saurians, yet while the existing fauna of the
temperate parts of North America is nearly destitute of aquatic
reptiles, with the exception of the turtles, it can boast, according
to Cope's lists, about fifty Mesozoic species, many of them of
gigantic size, and the number of known species is increasing every
year When it is taken in connection with these statistics, that while
we know all the modern species, we know but a small percentage of the
fossils, the discrepancy becomes still more startling. Further, from
the number of specimens and fragments found, it is obvious that these
great aquatic saurians were by no means rare; and that some of the
species at least must have been very abundant. Could we have taken our
post on the Mesozoic shore, or sailed over its waters, we should have
found ourselves in the midst of swarms of these strange, often
hideous, and always grotesque creatures.
Let us consider for a little some of the more conspicuous forms,
referring to our illustration for their portraits. Every text-book
figures the well-known types of the genera _Ichthyosaurus_ and
_Plesiosaurus_; we need scarcely, therefore, dwell on them, except to
state that the catalogues of British fossils include eleven species of
the former genus and eighteen of the latter, We may, however, notice
some of the less familiar points of comparison of the two genera. Both
were aquatic, and probably marine. Both swam by means of paddles; both
were carnivorous, and probably fed principally upon fishes; both were
proper reptiles, and breathed air, and had large and capacious lungs.
Yet with these points in common, no two animals could have been more
different in detail. The Ichthyosaurus had an enormous head, with
powerful jaws, furnished with numerous and strong teeth. Its great
eyes, strengthened by a circle of bony plates, exceeded in dimensions,
and probably in power of vision under water, those of any other
animal, recent or fossil. Its neck was short, its trunk massive, with
paddles or swimming limbs of comparatively small size, and a long
tail, probably furnished with a caudal fin or paddle for propulsion
through the water. The Plesiosaur, on the other hand, had a small and
delicate head, with slender teeth and small eyes. Its neck, of great
length and with numerous joints, resembled the body of a serpent. Its
trunk, short, compact, and inflexible, was furnished with large and
strong paddles, and its tail was too short to be of any service except
for steering. Compared with the Ichthyosaur, it was what the giraffe
is to the rhinoceros, or the swan to the porpoise. Two fishermen so
variously and differently fitted for their work it would be difficult
to imagine. But these differences were obviously related to
corresponding differences in food and habit. The Ichthyosaur was
fitted to struggle with the waves of the stormy sea, to roll therein
like modern whales and grampuses, to seize and devour great fishes,
and to dive for them into the depths; and its great armour-plated eyes
must have been well adapted for vision in the deeper waters. The
Plesiosaur, on the contrary, was fitted for comparatively still and
shallow waters; swimming near the surface with its graceful neck
curving aloft, it could dart at the smaller fishes on the surface, or
stretch its long neck downward in search of those near the bottom. The
Ichthyosaurs rolled like porpoises in the surf of the Liassic coral
reefs and the waves beyond; the Plesiosaurs careered gracefully in the
quiet waters within. Both had their beginning at the same time in the
earlier Mesozoic, and both found a common and final grave in its later
sediments. Some of the species were of very moderate size, but there
were Ichthyosaurs twenty five feet long, and Plesiosaurs at least
eighteen feet in length.
Another strange and monstrous group of creatures, the Elasmosaurs and
their allies, combined the long neck of Plesiosaurs with the swimming
tail of Ichthyosaurs, the latter enormously elongated, so that these
Creatures were sometimes fifty feet in length, and whale-like in the
dimensions of their bodies. It is curious that these composite
creatures belong to a later period of the Mesozoic then the typical
Ichthyosaurs and Plesiosaurs, as if the characters at one time
separated in these genera had united in their successors.
One of the relatives of the Plesiosaurs, the Pliosaur, of which genus
several species of great size are known perhaps realized in the
highest degree possible the idea of a huge marine predaceous reptile.
The head in some of the species was eight feet in length, armed with
conical teeth a foot long. The neck was not only long, but massive and
powerful, the paddles, four in number, were six or seven feet in
length and must have urged the vast bulk of the animal, perhaps forty
feet in extent, through the water with prodigious speed. The capacious
chest and great ribs show a powerful heart and lungs. Imagine such a
creature raising its huge head twelve feet or more out of water, and
rushing after its prey, impelled with perhaps the most powerful oars
ever possessed by any animal. We may be thankful that such monsters,
more terrible then even the fabled sea-serpent, are unknown in our
days. Buckland, I think, at one time indulged in the _jeu d'esprit_ of
supposing an Ichthyosaur lecturing on the human skull. "You will at
once perceive," said the lecturer, "that the skull before us belonged
to one of the lower orders of animals. The teeth are very
insignificant, the power of the jaws trifling, and altogether it seems
wonderful how the creature could have procured food." We cannot retort
on the Ichthyosaur and his contemporaries, for we can see that they
were admirably fitted for the work they had in hand; but we can see
that had man been so unfortunate as to have lived in their days, he
might have been anything but the lord of creation.
But there were sea-serpents as well as other monsters in the Mesozoic
seas. Many years ago the Lower Cretaceous beds of St. Peter's Mount,
near Maestricht, afforded a skull three feet in length, of massive
proportions, and furnished with strong conical teeth, to which the
name _Mosasaurus Camperi_ was given. The skull and other parts of the
skeleton found with it, were held to indicate a large aquatic reptile,
but its precise position in its class was long a subject of dispute.
Faujas held it to be a crocodile; Camper, Cuvier, and Owen regarded it
as a gigantic lizard. More recently, additional specimens, especially
those found in the Cretaceous formations of North America, have thrown
new light upon its structure, and have shown it to present a singular
combination of the character of serpents, lizards, and of the great
sea saurians already referred to. Some parts of the head and the
articulation of the jaws, in important points resemble those of
serpents, while in other respects the head is that of a gigantic
lizard. The body and tail are greatly lengthened out, having more then
a hundred vertebral joints, and in one of the larger species attaining
the length of eighty feet. The trunk itself is much elongated, and
with ribs like those of a snake. There are no walking feet, but a pair
of fins or paddles like those of Ichthyosaurus. Cope, who has
described these great creatures as they occur in the Cretaceous of the
United States, thus sketches the Mosasaur: "It was a long and slender
reptile, with a pair of powerful paddles in front, a moderately long
neck, and flat pointed head. The very long tail was flat and deep,
like that of a great eel, forming a powerful propeller. The arches of
the vertebral column were more extensively interlocked then in any
other reptiles except the snakes. In the related genus _Clidastes_
this structure is as fully developed as in the serpents, so that we
can picture to ourselves its well-known consequences; their rapid
progress through the water by lateral undulations, their lithe motions
on the land, the rapid stroke, the ready coil, or the elevation of the
head and vertebral column, literally a living pillar, towering above
the waves or the thickets of the shore swamps." As in serpents, the
mouth was wide in its gape, and the lower jaw capable of a certain
separation from the skull to admit of swallowing large prey. Besides
this the lower jaw had an additional peculiarity, seen in some snakes,
namely, a joint in the middle of the jaw enabling its sides to expand,
so that the food might be swallowed "between the branches of the jaw."
Perhaps no creatures more fully realize in their enormous length and
terrible powers the great Tanninim (the stretched-out or extended
reptiles) of the fifth day of the Mosaic record, then the Mosasaurus
and Elasmosaurus. When Mr. Cope showed me, a few years ago, a nearly
complete skeleton of Elasmosaurus, which for want of space he had
stretched on a gallery along two sides of a large room, I could not
help suggesting to him that the name of the creature should be
_Teinosaurus_[AF] instead of that which he had given. Marsh has
recently ascertained that the Mosasaurs were covered in part at least
with bony scales.
[AF] Heb. _Tanan_; Gr. _Teino_, _Tanuo_; Sansc. _Tanu_; Lat.
_Tendo_.--Ges. Lex.
[Illustration: LIFE IN THE MESOZOIC PERIOD.
Aquatic Reptiles and Cephalopods. _Reptiles._--Plesiosaur and
Osteopygis, Ichthyosaur, Teliosaur, Plesiosaur, Elasmosaur, Mosasaur
(in order of the heads from left to right).--_Cephalopods._--Ammonite,
Crioceras, Belemnites, Baculites, and Ammonites (in order from left to
right). The Reptiles after Hawkins and Cope's Restorations.]
These animals may serve as specimens of the reptilian giants of the
Mesozoic seas; but before leaving them we must at least invite
attention to the remarkable fact that they were contemporary with
species which represent the more common aquatic reptiles of the modern
world. In other words, the monsters which we have described existed
over and above a far more abundant population of crocodiles and
turtles then the modern waters can boast. The crocodiles were
represented both in Europe and America by numerous and large species,
most of them with long snouts like the modern Gavials, a few with
broad heads like those of the alligators. The turtles again presented
not only many species, but most of the aquatic subdivisions of the
group known in modern times, as for instance the Emydes or ordinary
fresh-water forms, the snapping turtles, and the soft-shelled turtles.
Cope says that the Cretaceous of New Jersey alone affords twenty
species, one of them a snapping turtle six feet in length. Owen
records above a dozen large species from the Upper Mesozoic of
England, and dates the first appearance of the turtles in England
about the time of the Portland stone, or in the upper half of the
Mesozoic; but footprints supposed to be those of turtles are found as
far back as the Trias. Perhaps no type of modern reptiles is more
curiously specialized then these animals, yet we thus find them
contemporaneous with many generalized types, and entering into
existence perhaps as soon as they. The turtles did not culminate in
the Mesozoic, but go on to be represented by more numerous and larger
species in the Tertiary and Modern. In the case of the crocodiles,
while they attained perhaps a maximum toward the end of the Mesozoic,
it was in a peculiar form. The crocodiles of this old time had
vertebrae with a hollow at each end like the fishes, or with a
projection in the front. At the end of the Mesozoic this was changed,
and they assumed a better-knit back, with joints having a ball behind
and a socket in front. In the Cretaceous age, species having these two
kinds of backbone were contemporaneous. Perhaps this improvement in
the crocodilian back had something to do with the persistence of this
type after so many others of the sea-lizards of the Mesozoic had
passed away.
Of the fishes of the Mesozoic we need only say that they were very
abundant, and consisted of sharks and ganoids of various types, until
near the close of the period, when the ordinary horny-scaled fishes,
such as abound in our present seas, appear to have been introduced.
One curious point of difference is that the unequally lobed tail of
the Palæozoic fishes is dropped in the case of the greater part of the
ganoids, and replaced by the squarely-cut tail prevalent in modern
times.
In the sub-kingdom of the Mollusca many important revolutions
occurred. Among the lamp-shells a little _Leptaena_, no bigger then a
pea, is the last and depauperated representative of a great Palæozoic
family. Another, that of the Spirifers, still shows a few species in
the Lower Mesozoic. Others, like Rhynchonella, and Terebratula,
continue through the period, and extend into the Modern. Passing over
the ordinary bivalves and sea-snails, which in the main conform to
those of our own time, we find perhaps the most wonderful changes
among the relatives of the cuttle-fishes and Nautili. As far back as
the Silurian we find the giant Orthoceratites contemporary with
Nautili, very like those of the present ocean. With the close
of the Palæozoic, however, the Orthoceratites and their allies
disappear, while the Nautili continue, and are reinforced by
multitudes of new forms of spiral chambered shells, some of them
more wonderful and beautiful then any of those which either preceded
or followed them. Supreme among these is the great group of the
_Ammonites_,--beautifully spiral shells, thin and pearly like the
Nautilus, and chambered like it, so as to serve as a float, but far
more elaborately constructed, inasmuch as the chambers were not simply
curved, but crimped and convoluted, so as to give the outer wall much
more effectual support. This outer wall, too, was worked into
ornamental ribs and bands, which not only gave it exquisite beauty,
but contributed to combine strength to resist pressure with the
lightness necessary to a float. In some of these points it is true the
Gyroceras and Goniatites of the Palæozoic partially anticipated them,
but much less perfectly. The animals which inhabited these shells must
have been similar to that of Nautilus, but somewhat different in the
proportion of parts. They must have had the same power of rising and
sinking in the water, but the mechanical construction of their shells
was so much more perfect relatively to this end, that they were
probably more active and locomotive then the Nautili. They must have
swarmed in the Mesozoic seas, some beds of limestone and shale being
filled with them; and as many as eight hundred species of this family
are believed to be known, including, however, such forms as the
_Baculites_ or straight Ammonites, bearing to them perhaps a relation
similar to that of Orthoceras to Nautilus. Further, some of the
Ammonites are of gigantic size, one species being three feet in
diameter, while others are very minute. The whole family of
Ammonitids, which begins to be in force in the Trias, disappears at
the end of the Mesozoic, so that this may be called the special age
of Ammonites as well as of reptiles.
Further, this time was likewise distinguished by the introduction of
true cuttle-fishes, the most remarkable of which were those furnished
with the internal supports or "bones," known as _Belemnites_, from a
fancied resemblance to javelins or thunder-bolts, a comparison at
least as baseless as that often made in England of the Ammonites to
fossil snakes. The shell of the Belemnite is a most curious structure.
Its usual general shape is a pointed cylinder or elongated cone. At
top it has a deep cavity for the reception of certain of the viscera
of the animal. Below this is a conical series of chambers, the
Phragmacone; and the lower half of the shell is composed of a solid
shelly mass or guard, which, in its structure of radiating fibres and
concentric layers, resembles a stalactite, or a petrified piece of
exogenous wood. This structure was an internal shell or support like
those of the modern cuttle-fishes; but it is difficult to account for
its peculiarities, so much more complex then in any existing species.
The most rational supposition seems to be that it was intended to
serve the triple purpose of a support, a float, and a sinker. Unlike
the shell of a Nautilus, if thrown into the water it would no doubt
have, sunk, and with the pointed end first. Consequently, it was not a
float simply, but a float and sinker combined, and its effect must
have been to keep the animal at the bottom, with its head upward. The
Belemnite was therefore an exceptional cuttle-fish, intended to stand
erect on the sea-bottom and probably to dart upward in search of its
prey; for the suckers and hooks with which its arms were furnished
show that, like other cuttle-fishes, it was carnivorous and
predaceous. The guard may have been less ponderous when recent then in
the fossil specimens, and in some species it was of small size or
slender, and in others it was hollow. Possibly, also, the soft tissues
of the animal were not dense, and it may have had swimming fins at the
sides. In any case they must have been active creatures, and no doubt
could dart backward by expelling water from their gill chamber, while
we know that they had ink-bags, provided with that wonderfully divided
pigment, inimitable by art, with which the modern Sepia darkens the
water to shelter itself from its enemies. The Belemnites must have
swarmed in the Mesozoic seas; and as squids and cuttles now afford
choice morsels to the larger fishes, so did the Belemnites in their
day. There is evidence that even the great sea-lizards did not disdain
to feed on them. We can imagine a great shoal of these creatures
darting up and down, seizing with their ten hooked arms their finny or
crustacean prey. In an instant a great fish or saurian darts down
among them; they blacken the water with a thick cloud of inky
secretion and disperse on all sides, while their enemy, blindly
seizing a few mouthfuls, returns sullenly to the surface. A great
number of species of Belemnites and allied animals have been
described; but it is probable that in naming them too little regard
has been paid to distinctions of age and sex. The Belemnites were for
the most part small creatures; but there is evidence that there
existed with them some larger and more formidable cuttles; and it is
worthy of note that, in several of these, the arms, as in the
Belemnites, were furnished with hooks as well as suckers, an
exceptional arrangement in their modern allies. It is probable that
while the four-gilled or shell-bearing cuttles culminated in size and
perfection in the Ammonitids of the Mesozoic, the modern cuttles of
the two-gilled and shell-less type are grander in dimensions then
their Mesozoic predecessors. It is, however, not a little singular
that a group so peculiar and apparently so well provided with means,
both of offence and defence, as the Belemnites, should come in and go
out with the Mesozoic, and that the Nautiloid group, after attaining
to the magnitude and complexity of the great Ammonites, should retreat
to a few species of diminutive and simply-constructed Nautili; and in
doing so should return to one of the old types dating as far back as
the older Palæozoic, and continuing unchanged through all the
intervening time.
The Crustaceans of the Mesozoic had lost all the antique peculiarities
of the older time, and had so much of the aspect of those of the
present day, that an ordinary observer, if he could be shown a
quantity of Jurassic or Cretaceous crabs, lobsters, and shrimps, would
not readily recognise the difference, which did not exceed what occurs
in distant geographical regions in the present day. The same remark
may be made as to the corals of the Mesozoic; and with some
limitations, as to the star-fishes and sea-urchins, which latter are
especially numerous and varied in the Cretaceous age. In short, all
the invertebrate forms of life, and the fishes and reptiles among the
vertebrates, had already attained their maximum elevation in the
Mesozoic; and some of them have subsequently sunk considerably in
absolute as well as relative importance.
In the course of the Mesozoic, as indicated in the last chapter, there
had been several great depressions and re-elevations of the
Continental Areas. But these had been of the same quiet and partial
character with those of the Palæozoic, and it was not until the close
of the Mesozoic time, in the Cretaceous age, that a great and
exceptional subsidence involved for a long period the areas of our
present continents in a submergence wider and deeper then any that had
previously occurred since the dry land first rose out of the waters.
Every one knows the great chalk beds which appear in the south of
England, and which have given its name to the latest age of the
Mesozoic. This great deposit of light-coloured and usually soft
calcareous matter attains in some places to the enormous thickness of
1,000 feet. Nor is it limited in extent. According to Lyell, its
European distribution is from Ireland to the Crimea, a distance of
1,140 geographical miles; and from the south of France to Sweden, a
distance of 840 geographical miles. Similar rocks, though not in all
cases of the precise nature of chalk, occur extensively in Asia and in
Africa, and also in North and South America.
But what is chalk? It was, though one of the most familiar, one of the
most inscrutable of rocks, until the microscope revealed its
structure. The softer varieties, gently grated or kneaded down in
water, or the harder varieties cut in thin slices, show a congeries of
microscopic chambered shells belonging to the humble and simple group
of Protozoa. These shells and their fragments constitute the material
of the ordinary chalk. With these are numerous spicules of sponges and
silicious cell-walls of the minute one-celled plants called Diatoms.
Further, the flinty matter of these organisms has by the law of
molecular attraction been collected into concretions, which are the
flints of the chalk. Such a rock is necessarily oceanic; but more then
this, it is abyssal. Laborious dredging has shown that similar matter
is now being formed only in the deep bed of the ocean, whither no sand
or mud is drifted from the land, and where the countless hosts of
microscopic shell-bearing protozoa continually drop their little
skeletons on the bottom, slowly accumulating a chalky mud or slime.
that such a rock should occur over vast areas of the continental
plateaus, that both in Europe and America it should be found to cover
the tops of hills several thousand feet high, and that its thickness
should amount to several hundreds of feet, are facts which evidence a
revolution more stupendous perhaps then that at the close of the
Palæozoic. For the first time since the Laurentian, the great
continental plateaus changed places with the abysses of the ocean, and
the successors of the Laurentian Eozoon again reigned on surfaces
which through the whole lapse of Palæozoic and Mesozoic time had been
separated more or less from that deep ocean out of which they rose at
first. This great Cretaceous subsidence was different from the
disturbances of the Permian age. There was at first no crumpling of
the crust, but merely a slow and long-continued sinking of the land
areas, followed, however, by crumpling of the most stupendous
character, which led at the close of the Cretaceous and in the earlier
Tertiary to the formation of what are now the greatest mountain chains
in the world. As examples may be mentioned the Himalaya, the Andes,
and the Alps, on all which the deep-sea beds of the Cretaceous are
seen at great elevations. In Europe this depression was almost
universal, only very limited areas remaining out of water. In America
a large tract remained above water in the region of the Appalachians.
This gives us some clue to the phenomena. The great Permian collapse
led to the crumpling-up of the Appalachians and the Urals, and the
older hills of Western Europe. The Cretaceous collapse led to the
crumpling of the great N.W. and S.E. chain of the Rocky Mountains and
Andes, and to that of the east and west chains of the south of Asia
and Europe. The cause was probably in both cases the same; but the
crust gave way in a different part, and owing to this there was a
greater amount of submergence of our familiar continental plateaus in
the Cretaceous then in the Permian.
Another remarkable indication of the nature of the Cretaceous
subsidence, is the occurrence of beds filled with grains of the
mineral Glauconite or "green-sand." These grains are not properly
sand, but little concretions, which form in the bottom of the deep
sea, often filling and taking casts of the interior and fine tubes of
Foraminiferal shells. Now this Glauconite, a hydrous silicate of iron
and potash, is akin to similar materials found filling the pores of
fossils in Silurian beds. It is also akin to the Serpentine filling
the pores of Eozoon in the Laurentian. Such materials are formed only
in the deeper parts of the ocean, and apparently most abundantly where
currents of warm water are flowing at the surface, as in the area of
the Gulf Stream. Thus, not only in the prevalence of Foraminifera, but
in the formation of hydrous silicates, does the Cretaceous recall the
Laurentian. Such materials had no doubt been forming, and such animals
living in the ocean depths, all through the intervening ages, but with
the exception of a few and merely local instances, we know nothing of
them, till the great subsidence and re-elevation of the Cretaceous
again allows them to ascend to the continental plateaus, and again
introduces us to this branch of the world-making process.
The attention recently drawn to these facts by the researches of Dr.
Carpenter and others, and especially the similarity in mineral
character and organic remains of some of the deposits now forming in
the Atlantic and those of the chalk, have caused it to be affirmed
that in the bed of the Atlantic these conditions of life and deposit
have continued from the Cretaceous up to the present time, or as it
has been expressed, that "we are still living in the Cretaceous
epoch." Now, this is true or false just as we apply the statement. We
have seen that the distinction between abyssal areas, continental
oceanic plateaus, and land surfaces has extended through the whole
lapse of geological time. In this broad sense we may be said to be
still living in the Laurentian epoch. In other words, the whole plan
of the earth's development is one and the same, and each class of
general condition once introduced is permanent somewhere. But in
another important sense we are not living in the Cretaceous epoch;
otherwise the present site of London would be a thousand fathoms deep
in the ocean; the Ichthyosaurs and Ammonites would be disporting
themselves in the water, and the huge Dinosaurs and strange
Pterodactyls living on the land. The Italian peasant is still in many
important points living in the period of the old Roman Empire. The
Arab of the desert remains in the Patriarchal period, and there are
some tribes not yet beyond the primitive age of stone. But the world
moves, nevertheless, and the era of Victoria is not that of the
Plantagenets or of Julius Cæsar. So while we may admit that certain of
the conditions of the Cretaceous seas still prevail in the bed of the
present ocean, we must maintain that nearly all else is changed, and
that the very existence of the partial similarity is of itself the
most conclusive proof of the general want of resemblance, and of the
thorough character of the changes which have occurred.
The duration of the Cretaceous subsidence must have been very great.
We do not know the rate at which the Foraminifera accumulate
calcareous mud. In some places, where currents heap up their shells,
they may be gathered rapidly; but on the average of the ocean bed,
afoot of such material must indicate the lapse of ages very long when
compared with those of modern history. We need not wonder, therefore,
that while some forms of deep-sea Cretaceous life, especially of the
lower grades, seem to have continued to our time, the inhabitants of
the shallow waters and the land have perished; and that the Neozoic or
Tertiary period introduces us to a new world of living beings. I say
we need not wonder; yet there is no reason why we should expect this
as a necessary consequence. As the Cretaceous deluge rose over the
continents of the Mesozoic, the great sea saurians might have
followed. Those of the land might have retreated to the tracts still
remaining out of water, and when the dry land again appeared in the
earlier Tertiary, they might again have replenished the earth, and we
might thus have truly been living in the Reptilian age up to this day.
But it was not so. The old world again perished, and the dawn of the
Tertiary shows to us at once the dynasties of the Mammalian age, which
was to culminate in the introduction of man. With the great Cretaceous
subsidence the curtain falls upon the age of reptiles, and when it
rises again, after the vast interval occupied in the deposition of the
green-sand and chalk, the scene has entirely changed. There are new
mountains and new plains, forests of different type, and animals such
as no previous age had seen.
How strange and inexplicable is this perishing of types in the
geological ages! Some we could well spare. We would not wish to have
our coasts infested by terrible sea saurians, or our forests by
carnivorous Dinosaurs. Yet why should these tyrants of creation so
utterly disappear without waiting for us to make war on them? Other
types we mourn. How glorious would the hundreds of species of
Ammonites have shone in the cases of our museums, had they still
lived! What images of beauty would they have afforded to the poets who
have made so much of the comparatively humble Nautilus! How perfectly,
too, were they furnished with all those mechanical appliances for
their ocean life, which are bestowed only with a niggardly hand on
their successors! Nature gives us no explanation of the mystery.
"From scarped cliff and quarried stone,
She cries--'A thousand types are gone.'"
But why or how one was taken and another left she is silent, and I
believe must continue to be so, because the causes, whether efficient
or final, are beyond her sphere. If we wish for a full explanation, we
must leave Nature, and ascend to the higher domain of the Spiritual.
CONDENSED TABULAR VIEW OF THE AGES AND PERIODS OF THE MESOZOIC.
Key to Symbols
### Duration of Ammonites and Belemnites.
=== Ages of Cycads and Pines.
--- Beginning of Age of Angiospermous Exogens.
+++ "And God created great reptiles, and every living moving
thing which the waters brought forth abundantly, and every
flying creature after its kind."
Time.
Ages. Periods. Animals and Plants.
MESOZOIC.
Cretaceous {Newer.{Maestricht beds; Fox Hill # - +
{ {and Pierre Groups of # - +
{ {Western America; Greensand # - +
{ {of New Jersey. # - +
{ # - +
{Middle.{Chalk; Benton and Dakota # Close of - +
{ {Groups of Western America. # Reptilian - +
{ # Ages. - +
{Older.{Lower Greensand and Gault; # - +
{ {Lower Clays of New Jersey # +
{ {and Alabama. # +
# +
Upper {N. Purbeck Beds. }Jurassic # Culmination +
Jurassic {M. Portland Limestone. } Beds of # of +
{O. Portland Sandstone. }Nebraska # Reptilian +
} and # Ages. +
Middle {N. Kimmeridge Clay, etc.}Colorado.# = +
Jurassic {M. Coralline Limestone. } # = +
{O. Calcareous Grit & } # = +
{ Oxford Clay. } # = +
# = +
Lower {N. Cornbrash & Forest } Lower # = +
Jurassic { Marble. }Jurassic # = +
{M. Great & Inferior } of # = +
{ Oolites., etc. } Utah, # = +
{O. Lias Clay and }Nevada, # = +
{ Limestone. } etc. = +
= +
{N. Keuper {Upper Triassic Appearance of = +
{ Sandstone, {Sandstones of Mammals = +
{ etc. {Prince Edward I., and = +
{M. Muschelkalk.{Connecticut, etc. Birds. +
Triassic { +
{O. Bunter {Lower Triassic Beginning of +
{ Sandstone. {Sandstones of Reptilian +
{ {Prince Edward I., Ages. +
{ {Connecticut, etc. +