Notwithstanding what has been done, it would still be premature to establish upon these numbers any conclusion relative to the theory of the earth, because they are not in sufficient proportion to the numbers of genera and species which may be buried in the strata of the earth. Hitherto the bones of the larger species have been chiefly collected, these being more obvious to agricultural labourers; while the bones of the smaller species are usually neglected, unless when they chance to fall into the hands of a naturalist, or when some particular circumstance, such as their excessive abundance in certain places, attracts the attention even of the common people. _Relations of the Species of Fossil Animals with the Strata in which they are found._ The most important consideration, that which, in fact, is the chief object of all my researches, and which establishes their legitimate connection with the Theory of the Earth, is to ascertain in what strata each species is found, and whether there may be some general laws, relative either to the zoological subdivisions, or to the greater or less resemblance of the species to those of the present day. The laws which have been recognised with respect to these relations are very distinct and satisfactory. In the first place, it is clearly ascertained that the oviparous quadrupeds appear much more early than the viviparous; that they are even more abundant, larger, and more varied, in the ancient strata than at the surface of the globe, as it exists at present. The Ichthyosauri, the Plesiosauri, several species of Tortoise, and several species of Crocodile, are found beneath the chalk, in the deposits commonly called _Jura formations_. The Monitors of Thuringia would be still older, if, according to the Wernerian School, the copper-slate in which they are contained, along with a great variety of fishes supposed to have belonged to fresh-water, is to be placed among the oldest beds of the secondary formations. The enormous crocodiles and the great tortoises of Maestricht, are found in the chalk formation itself; but these are marine animals. This earliest appearance of fossil bones seems, therefore, already to indicate, that dry lands and fresh waters had existed before the formation of the chalk deposits. But neither at this period, nor while the chalk was forming, nor even long after, have any bones of land-mammifera been encrusted; or, at least, the small number of these, which are alleged to have been found in strata of these dates, forms but a trifling exception. We begin to find bones of marine mammifera, namely, of lamantins and seals, in the coarse shelly limestone which covers the chalk in the neighbourhood of Paris; but there are still no bones of terrestrial mammifera.