72 INTRODUCTION. 



first place, the bed contain the remains of animals such as 

 now inhabit rivers, we know that it is " fluviatile " in its 

 origin, and that it must at one time have either formed an 

 actual river-bed, or been deposited by the overflowing of an 

 ancient stream. Secondly, if the bed contain the remains of 

 shell-fish, minute crustaceans, or fish, such as now inhabit 

 lakes, we know that it is "lacustrine," and was deposited 

 beneath the waters of a former lake. Thirdly, if the bed con- 

 tain the remains of animals such as now people the ocean, 

 we know that it is " marine " in its origin, and that it is a 

 fragment of an old sea-bottom. 



We can, however, often determine the conditions under 

 which a bed was deposited with greater accuracy than this. 

 If, for example, the fossils are of kinds resembling the marine 

 animals now inhabiting shallow waters, if they are accom- 

 panied 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 



