Most of the remains of land-animals, however, are found in deposits which have been laid down in water, and they owe their present position to the fact that their former owners were drowned in rivers or lakes, or carried out to sea by streams.

Birds, Flying Reptiles, and Flying Mammals might also similarly find their way into aqueous deposits; but it is to be remembered that many birds and mammals habitually spend a great part of their time in the water, and that these might therefore be naturally expected to present themselves as fossils in Sedimentary Rocks.

Plants, again, even when undoubtedly such as must have grown on land, do not prove that the bed in which they occur was formed on land.

Many of the remains of plants known to us are extraneous to the bed in which they are now found, having reached their present site by falling into lakes or rivers, or being carried out to sea by floods or gales of wind.

There are, however, many cases in which plants have undoubtedly grown on the very spot where we now find them.
Thus it is now generally admitted that the great coal-fields of the Carboniferous age are the result of the growth _in situ_ of the plants which compose coal, and that these grew on vast marshy or partially submerged tracts of level alluvial land.