rivers of the United States, peculiar species will be found in each basin, associated with others which are common to several basins. Thus, the Delaware River contains species not found in the Hudson. But, on the other hand, the pick. erel is found in both. Now, if all animals originated at one point, and from a single stock, the pickerel must have passed from the Delaware to the Hudson, or vice versa, which it could only have done by passing along the sea-shore, or by Leaping over large spaces of terra firma; that is to say, in both cases it would be necessary to do violence to its organi. zation. Now, such a supposition is in direct opposition to the immutability of the laws of Nature.

450. We shall hereafter see that the same laws of distribution are not limited to the actual creation only, but that they have also ruled the creations of former geological epochs, and that the fossil species have lived and died, most of them, at the place where their remains are found.

451. Even Man, although a cosmopolite, is subject, in a certain sense, to this law of limitation. While he is every where the one identical species, yet several races, marked by certain peculiarities of features, are recognized; such as the Caucasian, Mongolian, and African races, of which we are hereafter to speak. And it is not a little remarkable, that the abiding places of these several races correspond very nearly with some of the great zoological regions. Thus we have a northern race, comprising the Samoyedes in Asia, the Laplanders in Europe, and the Esquimaux in America, corresponding to the arctic fauna, (400,) and, like it, identical on the three continents, having for its southern limit the region of trees, (422.) In Africa, we have the Hottentot and Negro races, in the south and central portions respectively, while the people of northern Africa are a'lied to their neighbors in Europe; just as we have seen to be the case with the zoölogical fauna in general,

(403.) The inhabitants of New Holland, like its animals, are the most grotesque and uncouth of all races, (433.)

452. The same parallelism holds good elsewhere, though not always in so remarkable a degree. In America, especially, while the aboriginal race is as well distinguished from other races as is its flora, the minor divisions are not so decided. Indeed, the facilities, or we might sometimes rather say necessities, arising from the varied supplies of animal and vegetable food in the several regions, might be expected to involve, with his corresponding customs and modes of life, a difference in the physical constitution of man, which would contribute to augment any primeval differences. It could not indeed be expected, that a people constantly subjected to cold, like the people of the North, and living almost exclusively on fish, which is not to be obtained without great toil and peril, should present the same characteristics, either bodily or mental, as those who idly regale on the spontaneous bounties of tropical vegetation.

CHAPTER FOURTEENTH

GEOLOGICAL SUCCESSION OF ANIMALS; OR, THEIR DISTRIBUTION IN TIME.

SECTION I.

STRUCTURE OF THE EARTH'S CRUST.

453. THE records of the Bible, as well as human tradition, teach us that man and the animals associated with him were created by the word of God; "the Lord made heaven and earth, the sea, and all that in them is;" and this truth is confirmed by the revelations of science, which unequivocally indicate the direct interventions of creative power.

454. But man and the animals which now surround him are not the only kinds which have had a being. The surface of our planet, anterior to their appearance, was not a desert. There are, scattered through the crust of the earth, numerous animal and vegetable remains, which show that the earth had been repeatedly supplied with, and long in habited by, animals and plants altogether different from those now living.

455. In general, their hard parts are the only relics of them which have been preserved, such as the skeleton and teeth of Vertebrates; the shells of the Mollusks and Radiata; the shields of the Crustaceans, and sometimes the wing-cases of Insects. Most frequently they have lost their original

chemical composition, and are changed into stone; and hence the name of petrifactions or fossils, under which latter term are comprehended all the organized bodies of former epochs, obtained from the earth's crust. Others have entirely disappeared, leaving only their forms and sculpture impressed upon the rocks.

456. The study of these remains and of their position in the rocks constitutes PALEONTOLOGY; one of the most essential branches of Zoology. Their geological distribution, or the order of their successive appearance, namely, the distribution of animals in time, is of no less importance than the geographical distribution of living animals, their distribution in space, of which we have treated in the preceding chapter. To obtain an idea of the successive creations, and of the stupendous length of time they have required, it is necessary to sketch the principal outlines of Geology.

457. The rocks* which compose the crust of our globe are of two kinds :

1. The Massive Rocks, called also Plutonic or Igneous Rocks, which lie beneath all the others, or have sometimes been forced up through them, from beneath. They were once in a melted state, like the lava of the present epoch, and on cooling at the surface formed the original crust of the globe, the granite, and later porphyry, basalt, &c.

2. The Sedimentary or Stratified Rocks, called also Neptunic Rocks, which have been deposited in water, in the same manner as modern seas and lakes deposit sand and mud on their shores, or at the bottom.

458. These sediments have been derived partly from the disintegration of the older rocks, and partly from the decay of plants and animals. The materials being disposed in

* Rocks, in a geological sense, include all the materials of the earth, the loose soil and gravel, as well as the firm rock.

layers or strata, have become, as they hardened, limestones, slates, marls, or grits, according to their chemical and mechanical composition, and contain the remains of the animals and plants which were scattered through the waters.*

459. The different strata, when undisturbed, are arranged one above the other in a horizontal manner, like the leaves of a book, the lowest being the oldest. In consequence of the commotions which the crust of the globe has undergone, the strata have been ruptured, and many points of the surface have been elevated to great heights, in the form of mountains; and hence it is that fossils are sometimes found at the summit of the highest mountains, though the rocks containing them were originally formed at the bottom of the sea. But even when folded, or partly broken, their relative age may still be determined by an examination of the ends of the upturned strata, where they appear or crop out in succession, at the surface, or on the slopes of mountains, as seen in the diagram, (Fig. 154.)

460. The sedimentary rocks are the only ones which have been found to contain animal and vegetable remains. These are found imbedded in the rock, just as we should find them in the mud now deposited at the bottom of the sea, if laid dry. The strata containing fossils are numerous. The comparison and detailed study of them belongs to Geology, of

Underneath the deepest strata containing fossils, between these and the Plutonic rocks, are generally found very extensive layers of slates without fossils, (gneiss, mica-slate, talcose-slate,) though stratified, and known to the geologist under the name of Metamorphic Rocks, (Fig. 154, M,) being probably sedimentary rocks, which have undergone considerable changes. The Plutonic rocks, as well as the metamorphic rocks, are not always confined to the lower levels, but they are often seen rising to considerable heights, and forming many of the loftiest peaks of the globe. The former also penetrate, in many cases, like veins, through the whole mass of the stratified and metamorphic layers, and expand at the surface; as is the case with the trap dykes, and as lava streams actually le at the present era, (Fig. 154, T. L.)