LESSON III.

THE AGE OF CRABS AND CORALS.

“And delving in the outworks of this worldAnd little crevices that they could reach,Discovered certain bones laid up and furledUnder an ancient beach.”

“And delving in the outworks of this world

And little crevices that they could reach,

Discovered certain bones laid up and furled

Under an ancient beach.”

—Ingelow.

The earth-building period which followed the dawn of life is called the “time of ancient life.” Our lesson about this period will be like unlocking the gate to some beautiful domain, giving a glance at its delights, but leaving the wayfarer whom we have brought thus far on his journey, still standing without, yet now, no doubt, with ability and desire to enter.

This ancient-life time is, so far as we know, the longest of all the earth-building periods. It has the thickest deposits of rock, and includes the most numerous ages, or great successive changes. It also retains in its rocks numerous fossils, or casts of formerly living things, both animal and vegetable.In coming lessons we shall discuss what fossils are, and describe some of these ancient plants and animals.

THE WATER-SPRITES.

When this new age of the world opened, we find that there was plenty of life, and that there were many creatures akin to some that we have living to-day. To enjoy that time of the world we should have been no longer Afrites, or flame-spirits, for the reign of the fire was over; we should have been Pixies, and able to wander at our will among the plants and animals in the water. There we should have noticed that there were many animals of the articulate or jointed class—creatures that have no backbones; and we should have seen that the plants were sea-weeds of various kinds.As the ages of this great time moved on, creatures with vertebræ forming backbones appeared, and the land had vegetation. There were reeds, rushes, lichens, ferns, mosses, plants of the toad-stool kind, and great trees such as are now not found on the earth. Some of the rushes called calamites were larger than the great bamboo.

The first age of this great time is called the Cambrian, from the outcrop of its rocks in North Wales, the ancient Cambria. The name Huronian has also been applied to it, as these rocks largely appear in the region about Lake Huron. In this age new land rose above the ocean. The waters were still warm, and the atmosphere was hazy and full of moisture, hot, but without clear sunlight. The animals were corals and crabs; the vegetables were sea-weeds. The rocks of the Cambrian are chiefly sandstone and slate, and we find the fossils not scattered through all the rocks, but in layers, so that some ledges of rock are nearly destitute of organic remains, and then come others crowded with fossils of animals and vegetables.

Among the earliest and most curious of the fossils are the lingulæ. These are bivalve[9]shells, about the size and shape of your finger-nail. The lingula was fastened to the sand bed by a fleshy stem. Opening its valves, it put forth a fine fringe which served it as fingers for gathering its food from the waters, much as barnacles do.[10]The lingulæ belong to the group of lamp shells, and have existed through all the ages from the Cambrian until now, as they swarmat the present day in the China seas. Along with the busy little lingulæ lived many varieties of crabs, cuttle-fish, star-fish, and many kinds of corals.

Probably there were not many insects in this period: only a few fossils of large insects somewhat like dragon-flies and May-flies have been found. There were no birds, and the great forests of reeds and club-mosses were silent, unless the few insects could produce a chirping sound. Possibly their wings and bodies were gaily colored as those of the dragon-flies are to-day.

No doubt, also, many of the crustaceans of this period were very ornate in their colors, and in the arrangement of bands, knobs, and ridges on their shells. The numerous corals building in the shallow seas, and carrying their reefs up into the light on the surface, waved purple, orange, and crimson filaments from their limestone towers, until the waters looked like garden beds in full bloom.

Among the earliest fossils are worm-casts,[11]from which we learn that even so long ago the worms were helping to build the world. The sponges shared the shallow seas with the corals.

Next came the Silurian age, named as we know from a part of Wales where its rocks lie bare. This was a very long age, and is divided into upper and lower Silurian. During all this time the world was becoming richer and richer in life, both of animals and vegetables, and of both land and sea. We find strangely beautiful fossils of this age, as, for instance, the stone lilies. No form of life seemed for a time so hardyand so rich in variety as these stone lilies. These were not plants, but animals, and yet they looked more like beautiful snowy flowers than like animals.

In very deep water of the present day we find some few species of these crinoids, or stone-lily animals, and from them we can understand those of the ancient time. They grew rooted in one place, waved on long, pliant stems, and from their snowy cups spread forth filaments that looked like delicate stamens and pistils. Swimming about among the stone lilies, went the nautilus, relative of our “paper nautilus” of which the poet sings:—

“This is the ship of pearl, which poets feignSails the unshadowed main—The venturous bark which flingsOn the sweet summer wind its purpled wings,In gulfs enchanted where the siren sings,And coral reefs lie bare,Where the cold sea-maids rise to sun their streaming hair.”

“This is the ship of pearl, which poets feign

Sails the unshadowed main—

The venturous bark which flings

On the sweet summer wind its purpled wings,

In gulfs enchanted where the siren sings,

And coral reefs lie bare,

Where the cold sea-maids rise to sun their streaming hair.”

The nautilus of the Silurian time perhaps looked quite as lovely and harmless, yet really was a mighty monster, devouring millions of its fellow-denizens of the deep. To-day we see a relation of this old-time nautilus, in our cuttle-fish, sometimes called the devil-fish.

To the Silurian age belong the written stones. The tiny fossils imbedded in these rocks are like little coal-black stains, which appear as minute writing in an unknown tongue. These small cells are indeed writing, and help us to learn the story of the ancient world.

The corals increased greatly in the Silurian age, and extended far up to the polar regions, where corals are now unknown.In these early ages the chief home of life was in the sea. The waters brought forth living things before the earth produced them, while the creatures of the air, the birds and insects, came later still. Two very important facts are here to be noted: Just as the Silurian age was closing, several kinds of fish-like creatures appeared, the first vertebrate or backboned animals.

Let us imagine ourselves back in that age, as Pixies, or water-sprites. Suppose that we are in a warm, shallow, almost waveless sea, over which the sunshine pours, warm and mellow, through thin haze. We are sitting on a ledge of coral, and from every tiny limestone tower about us opens and waves a radiant creature, purple, gold, green, or crimson. Among the corals grow the tall and stately stone lilies, rolling back their petal-like valves, and waving forth long white plumes. We gather tiny live things from the water and offer them to the stone lilies, and they grasp them in their snowy hands.

But now we see a monster coming towards us, a new creature such as we have never seen before! It swims strongly, has a thick skin, great jaws filled with big teeth, and we perceive that it has its bones inside its body, not outside, as the crustaceans do. It sweeps past a bed of pretty little lingulæ and crops off fifty of them at a mouthful! It darts up to our lovely stone lily, and bites it from its pearl-white stem! Yonder comes a crab swimming along at ease, a prophecy of a king-crab, that will come many ages after. The fish-like monster takes him at a mouthful.

We Pixies are angry at this devastation; we cry, “Wehope you will try to eat a trilobite[12]and choke yourself!” But here comes an unlucky trilobite, and the new monster crushes it in its great jaws! It would eat us, only we are Pixies, creatures of myth, mere bubbles. As it is, we hide in our coral groves, and weep over our lost lingulæ and stone lilies. These fish-like creatures reign as kings. They multiply and devour, and in the Devonian age, which comes next, they become more like true fishes.

This Devonian age comes with mighty changes. We Pixies feel the sea-beds rock with earthquakes. We fly to the rivers, and find the land rent with volcanoes. We hasten to the crests of the waves,—for the torrents of lava rush along the shores and far out into the ocean,—and we see the Afrites laughing to find vast plains of land where waters had been. We hope that all these convulsions have destroyed the greedy, cruel fish. But no; we go deep into our sea-homes, and find most of the crabs and nautili and stone lilies gone, and the fish more abundant than ever!

And now we Pixies feel that the new age has come, and we rise to the sea-surface to look about, and we find new land in many lovely islands, and there are vast swamps full of reeds and club-mosses. Green lowland jungles laugh in bright sunlight, among warm, clear, blue seas, where the corals that we love grow to their greatest glory. No more soft-shelled crustaceans and trilobites: have the fishes eaten them all? If we make an excursion to the land to see if any fairies live there, we find no flowers, but there are very beautiful trees.

The great work of this Devonian age seems to be the rapid laying down of beds of red sandstone. This red sandstone, deposited by the waters, finally rises into vast continents, joining island to island, and spreading out a rich soil, very fit for vegetable life. Vegetation creeps away beyond the polar circles; for in this time the climate of the earth is nearly uniform.

Let us fancy we meet an Afrite, and say to him, “Of what use is all this land and vegetation?”

He replies, “O Pixy! a new age is coming,—the age of coal. In it vast beds of coal will be laid down to feed future fires for a creature called man. These beds will have oil, gas, naphtha, all things in which we Afrites rejoice. These carbon beds will be merely storehouses of well-cooked vegetation, for warming and lighting a world.”

But as we Pixies stand and talk with Afrites at the limit where land and water meet, what do we see? We see thousands of insects in the air and creeping on the ground,—cockroaches, dragon-flies, weevils. And now, oh, wonder of wonders! what fearful thing is this?A Reptile has appeared!

Frogs and toads of curious patterns have foreshadowed him, but the true reptile was the first vertebrate lung-breathing animal. You perceive it is a vast advance on earlier forms, for a creature to have a nose, to be able to inhale air through its nostrils!

The life-filled, tree-filled Carboniferous age, with its continents was long, very long; and now, when life seemed everywhere to dominate, these continents slowly sank beneaththe waters, and the Permian age came on,—the age of the death and burial of a busy world,—the last age of the ancient life time. The sinking was slow at first, so slow that trees grew above the buried trees; but at last the sinking hastened, and stones and sand and surf dashed and rolled above the forests, and the Coal age was drowned.

The reason of this sinking was, that the interior of the globe had continued to cool and harden, and with cooling shrank from the crust, which collapsed in great wrinkles. The collapse was slow, because much of the interior rock was in a wax-like condition, and crowded up to fill the rents left in the downward pressure of the earth-crust. The heat, pressure, collapse, half-fluid state, explain to us many of the curiosities of geologic formations.

After these convulsions the surface again arose, land lifted above the water, and the Permian age exhibited a flora very like that of the preceding age. The great frogs, toads, and lizards increased in size and numbers. The convulsions of the Permian had not destroyed all land life, and probably the sea-depths with their inhabitants had been but little effected. The buried forests of the previous age were slowly changed into the coal-beds of to-day, and in them we find, held for our study, seeds, roots, leaves, insects, and footprints, belonging to the long-gone ancient life time.

FOOTNOTES:[9]Nature Reader, No. 1, Lesson 39.[10]Nature Reader, No. 2, Lesson 33.[11]Nature Reader, No. 2, Lesson 12.[12]See Lesson XVI., p.119.

[9]Nature Reader, No. 1, Lesson 39.

[10]Nature Reader, No. 2, Lesson 33.

[11]Nature Reader, No. 2, Lesson 12.

[12]See Lesson XVI., p.119.

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