THE AGE OF REPTILES.

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that they did so in reality. At the same time the apparent suddenness of very great changes in life-forms shows, according to many men of science, indications of another and deeper Law of Introduction not yet firmly grasped. There is much that is now inexplainable on both sides.

Mesozoic, or middle, time was made remarkable by its vast numbers of reptiles and their huge and monstrous forms. It is called, in reference to animal life, the Age of Reptiles. They were sometimes eighty feet in length. There were monstrous sea-serpents, and a great variety of reptiles twenty to fifty feet in length, that sported about the sea-shores, that roamed over the land, the terror of other animals that often became their prey, or that fed on the foliage of trees. Others had immense wings like the bat. The evidence appears to show that the lands were covered with verdure and swarmed with animal life, of which it is probable comparatively few specimens have been preserved in the Valley.

Many of these monster reptiles have been preserved in the then rock-making regions of Kansas and Nebraska. The types, however, are the same in all lands; for, until after the greater mountain-making era, a warm-temperate or subtropical climate reigned far within the Arctic Circle, and great quantities of coal were made there and in various parts of the earth. The ancient genera and species of the animals of the sea had disappeared under the changed conditions, but more modern forms, for the most part, took their places, although some classes quite disappeared. There was a great development of insects, and birds, chiefly aquatic species, became numerous, while, about the middle of the Mesozoic, the class of vertebrates to which man belongs, mammals, or those that suckle their young, appeared. These gradually. increased and became quite numerous toward the close of Mesozoic time, while reptiles as steadily decreased and passed over but few of their representatives to the Cenozoic, or Recent Period.

From the opening of that period there was a steady and rapid modernizing of animal life in keeping with the general approach to present conditions of continents, seas, and the atmosphere. Vast quantities of coal were magazined from the carbonic-acid gas of the atmosphere just before the Rocky Mountains were raised, or during that process, and the air was fitted to nourish higher and more intense forms of life. The shores of the Gulf abounded in immense whales, and in the rocks of the Western Valley elephants, rhinoceroses, and many other huge animals, which yet approached modern types, are found. One of the most interesting is the horse, which commences in the Eocene, or opening period of Recent Time, as small as a fox, and with four toes. As time passes the horse becomes larger, till it is gigantic, and, one by one, loses its toes till but one remains, the nail of which expands into the hoof as we now find it. It is an interesting revelation of gradual changes of form and quality. At the same time there flourished in the Valley hyenas, wolves, tigers, panthers, tapirs, hogs, camels, lamas, deer, hares, squirrels, beavers, and many other ancestors of modern animals of almost every class.

After the Glacial Period many of these disappeared from the western continent. It is somewhat curious to note. that many plants and animals that first appeared in North America appear in the next age and group of rocks of the Old World, as if this was at some periods the Old World which colonized Europe as the then New World. There has been found reason to believe that the first land was raised along the north of the Valley; the Alleghanies are thought to be the oldest of the large mountain-ranges; and probably the upper part of the Valley east of the Missouri was the most extensive region whose rock-making and general structure was completed immediately after the Age of Coal. It would not, therefore, be surprising if it was ready for the habitation of some classes of animals before Europe, which

MAN THE IDEAL ANIMAL.

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continued to pass through important changes until late in geological time. Yet many of these animals, after a long career here, wholly disappeared while still continuing in Europe.

When the Glacial Period came on it is natural to suppose that the higher land animals retreated southward before it, and many of them survived it to perish before man could be benefited by them-as the horse, reindeer, and others. The animal kingdom continued, however, to be represented by huge and powerful animals, and to raise some of its classes in the scale of organization till man appeared. He was the Ideal Animal. Their progress had ever been (it is not proven how) from feeble to lively sensation; from few and confused parts and small measures of energy to many and highly elaborated sets of powers; from a few scattered fascicles of nerves to the extensive and well-protected system of the vertebrates; and the prone body and barrel form of the fish was soon excelled by a more and more erect head, while the long posterior body was shortened until only legs were left, while all the noble vital organs were raised in power and crowded into the front until the head was raised perpendicularly above them, and the fore legs were no longer instruments of locomotion but servants of the brain.

This uprightness, with the face and forehead on a perpendicular line with the front of the body, reached the limit of possible improvement in the frame, while the intelligence of man joined all the instincts and limited perceptions and passions of all the animal world in one mind, with undefined and fairly unlimited possibilities of power and growth, to which was added a class of faculties constituting his highest value-moral powers-the love of virtue and truth. As there can be no nobler frame in the animal world, so there can be no being essentially greater than man, in his highest and peculiar gifts, unless by an expansion of the same qualities. There was greater intelligence and power in the Principle

that planned and produced the world, but since man can comprehend the work he must be of the same nature as the Workman.

CHAPTER VII.

GENERAL VIEW OF THE FINISHED VALLEY.

We have seen how heat and the loss of heat provided the inconceivable force in the crust of the earth required for the immense changes of every geological age. The vastness of the power is very evident, as also is the restraint laid on it. It was, so to speak, tamed and made to work in harness. What it has done shows how easily it could have become a destroyer instead of a builder. Yet it worked slowly, cautiously, never getting ahead of its chemical, mechanical, and organic associates. Chemical attractions and repulsions made and unmade rocks, and stored up minerals at the points where the forethought that guided volcanic force and the power arising from contraction designated, winds and waves, sun and storm, torrent and gravity made rock in the proper places, and the Life Force worked with unflagging zeal in vegetable and animal to supply the most useful rocks and to store the richest treasures. Finally, cold came to do a most important surface work and then retired, leaving the slow falling and rising of the levels, the waters, dews, rains, and the sun to re-arrange the drift, vital energy to re-people it with animal and vegetable life, and present it finished to man when he should appear.

We have now to observe its general features as completed. From north to south the extreme of its length is about 2,000 miles; the extreme descent through its center in that distance being a little over 1,600 feet. The descent is nowhere very abrupt, although about three fourths of it are accomplished in the upper part of the Valley, from the head of the Mississippi to the mouth of the Missouri. The very gradual fall from