tiation which causes the resemblance of the higher incomplete, to the lower complete forms. To limit ourselves to one example: it is quite incomprehensible why the ear-bones of the mammal should be developed, by the circuitous process of the formation of germinal fissures, if it were a mere question of histological and morphological differentiation. This explanation fails also with regard to the whole class of the phenomena of purposeless and abortive organs, and, finally, the evolutionary type" itself as it rules the groups and regulates individual development, still remains without an explanation.

IV.

The Animal World in its Historical and Paleontological Development It is so easy to observe that the earth's crust, from the deepest valleys to the highest mountain top contains innumerable animal remains, that even antiquity could not fail to notice it. But some two thousand years passed by before a correct knowledge was attained of the relations of these remains to the present world. Some thought they were sports of nature, products of creative power leading to no special object, but in a certain measure to be regarded as exercises preliminary to the actual creation of life; others considered the fossils as remains of living creatures, indeed, but of such as still existed, and which had been destroyed by overflows and subsequent withdrawals of the sea. The legend of the universal deluge, especially, derived great support from this second opinion. Only when, at the end of last century, the stratification of the earth's crust was revealed to science, after the outlines of a history of the solar system and of a special history of the earth or geology had been indicated by Kant and Laplace, only then arose the possibility and necessity of a real palæontology, or knowledge of prehistoric life. At the beginning of this century it was discovered that the fossils corresponding with the stra

tification of the earth's crust follow each other in regular sequence, and that in this sequence they differ from the present creation, as they do from each other.

We must make ourselves acquainted with the order of succession of these strata. They are the shelves in which the vegetable and animal remains lie stored. To arrange them was certainly possible only by taking the organisms which they contained as guides or clues. We, however, shall take this arrangement as our data,. and, with the object we have in view, we shall naturally consider only those strata and rocks in which fossilsusing this word in its widest interpretation—are or might be contained, those, namely, which are proved to be sedimentary, i.e. aqueous deposits. Our information is limited to a great part of Europe, numerous districts of America, and scattered points of the rest of the world. The following table gives the the arrangement of the sedimentary strata from above downwards :—

6. Triassic formation or New Red Sandstone.

Keuper or Variegated Marls.
Muschelkalk.

Variegated Sandstone.

7. Permian formation or Dyas

Zechstein (Magnesian Limestone or Dolomitic Conglomerate).
Rothliegendes or Red Conglomerate.

8. Carboniferous formation.

Coal Measures.

Millstone Grit.

Mountain Limestone.

9. Devonian formation.
10. Silurian formation.
II. Cambrian formation.

12. Laurentian formation.

Although we are not writing on geology, a short explanation of these strata will be requisite, as their mutual relations also throw light on the nature and distribution of the contemporaneous organisms. All displacements of earth which we now see occurring by means of rain, rivers, sea and other natural forces which have taken place in historic times, in short, in the so-called Present, such as the great delta deposits, and the moraine formations of our glaciers, are ascribed to the Alluvium.

It was formerly supposed that its limits might be distinguished from the Diluvium by the appearance of man, but as it is now, and always has been impossible to affirm anything positive respecting that epoch, and as, although a portion of the organisms of which the remains occur in the Diluvial strata is extinct, much more still exists, these two formations are inseparably intermingled.

To the Diluvium belong the vast mud deposits of the great rivers, alternating with sand banks, the clay and loess formations caused by the removal of the soil

by the drainage of the glaciers and the floods of running water, which at one time increased periodically to a degree truly colossal. The diluvial period, as it seems, includes, both in Europe and America, a repeated glacification of countries and vast portions of the world, of which the present state of Greenland may now give some idea.

The period of the series of strata, comprised under the name of the tertiary formation, may be regarded as that during which, at least, the skeleton of the present continents finally attained its integral configuration. Within its limits fall the erection and upheaval of the great mountain chains, the Cordilleras, Alps, Himalayas, and others; the outlines of the continents were, meanwhile, in constant movement. This phenomenon, however, persists throughout all formations, and, as the geological characteristic of the tertiary formation, more stress should be laid on the separation of the earth's surface into climatic zones, approximating to the zones of the present age. The names of the subdivisions are intended to indicate the relation of the animals then living to those of our world, as it was supposed that in the eocene the first animals identical with present species were to be found, more in the miocene, and, yet more, in the pliocene.

To the chalk formation belong rocks of very various kinds, which can be reduced to one great geological period by means of their contents. If the quartzose sandstone of Saxon Switzerland represents this formation in the centre of Germany, it is from the white chalk of England and Northern France that it took its name. In America, the sandstone has been in a great measure