yS INTRODUCTION. 



the fossils are of kinds resembling the marine animals now inhabiting 

 shallow waters, if they are accompanied by the detached relics of 

 terrestrial organisms, or if they are partially rolled and broken, we 

 may conclude that the fossiliferous 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), we 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 accumula- 

 tion 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 wanting, 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 conclusions 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 undoubt- 

 edly 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 gener- 

 ally admitted that the great coal-fields of the Carboniferous age are 

 the result of the growth in situ of the plants which compose coal, 



