CONCLUSIONS TO BE DRAWN FROM FOSSILS. 41 



ferous deposit was laid down in a shallow sea, in the immediate 

 vicinity of a coast-line, or as an actual shore-deposit. If, again, 

 the remains are those of animals such as now live in the deeper 

 parts of the ocean, and there is a very sparing intermixture of 

 extraneous fossils (such as the bones of birds or quadrupeds, 

 or the remains of plants), w r e may presume that the deposit is 

 one of deep water. In other cases, we may find, scattered 

 through the rock, and still in their natural position, the valves 

 of shells such as we know at the present day as living buried 

 in the sand or mud of the sea-shore or of estuaries. In other 

 cases, the bed may obviously have been an ancient coral-reef, 

 or an accumulation of social shells, like Oysters. Lastly, if we 

 find the deposit to contain the remains of marine shells, but 

 that these are dwarfed of their fair proportions and distorted 

 in figure, we may conclude that it was laid down in a brackish 

 sea, such as the Baltic, in which the proper saltness was want- 

 ing, owing to its receiving an excessive supply of fresh water. 



In the preceding, we have been dealing simply with the 

 remains of aquatic animals, and we have seen that certain con- 

 clusions can be accurately reached by an examination of these. 

 As regards the determination of the conditions of deposition 

 from the remains of aerial and terrestrial animals, or from 

 plants, there is not such an absolute certainty. The remains 

 of land-animals would, of course, occur in "sub-aerial" deposits 

 that is, in beds, like blown sand, accumulated upon the land. 

 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 having been 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 undoubt- 

 edly 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 



