3. _This class is much less chemical, indeed very little so, in its structure._ It is the result of mechanical deposition, after the chemical action had nearly ceased in the great primitive and retiring abyss.
4. _These rocks abound more in fragments of other rocks, and in the remains of organized beings, than the preceding class._ This would be natural, as a greater extent of the earth's surface would be exposed to the elements, and thus the destruction would be greater: and as the condition of the earth was better for sustaining sensitive beings, these would of course be more abundant both in _kind_ and _number_.
It is also well ascertained, from the fossil remains found in this class of rocks, that during their deposition, there existed many species of animals and plants which do not now exist: that many of the animals were _monsters_ of incredible size and voracity; of such hugeness, grossness, and ferocity as were suitable to the then prevailing condition of the earth.
The researches of the last ten or fifteen years, in England, have brought to light the skeletons of animals, approaching the _lizard genus_, from _sixty to seventy feet long_!! They are abundant in England, and occasionally found on the continent. Who can say, but that the other genera of animals then existing, were also as much more vast, and misshapen than their present existing types? A single glance at the _geological reminiscences_ of this ancient period must convince any observer, that the vegetable, and specially the animal genera then existing were really astonishing both in _size_, _shape_, and _nature_.
It becomes a question of some interest, whether these huge animals ceased to exist, having found their graves in this secondary class of rocks, before the existence of man?
There are many reasons which induce a supposition they did cease to exist. Man could scarcely have been safe in the land of these wonderful creatures. Moreover, it is probable their constitutions were adapted to the condition of the world at this period, which we suppose to have been more gross in its air, and water, and more ardent in its climate; as it had not yet settled, and dried; and the waters had not yet sufficiently subsided, to render the earth the abode of the more delicate land-animals, birds, and specially man. It is probable the earth was marshy, with numerous inland lakes, to a considerable extent; the waters still somewhat turbid; the air gross and moist; and the temperature still very high. Such a state of the planet would suit the constitutions of such monsters as the _ichthyosaurus_, and _plesiosaurus_, which would perish as the condition of the globe became more pure, and its temperature reduced.