54 PRINCIPLES OF PALAEONTOLOGY. 



contains 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 riverbed, 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 contain 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 accompanied 

 by the detached relics of terrestrial organisms, or if they are 

 partially rolled and broken, we may conclude that the fossil- 

 iferous 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 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 



