68 ON THE REVOLUTIONS OF 



very anciently formed, and generally composed of sand and round 

 flints, and which were probably the first alluvial deposites of the 

 ancient world. We find with them certain lost species of known 

 kinds, but in small numbers, and some oviparous quadrupeds and 

 fresh- water fishes. The beds which contain them are always more or 

 less covered over by the shifting beds, filled with shells and other 

 marine productions. 



Tire most celebrated of these unknown species, which belong to 

 the known kinds, or to kinds very much resembling those that are 

 known, such as the fossil elephant, the rhinoceros, the hippopotamus, 

 and the mastodons, are not found amongst the more ancient kinds. 

 It is only in the shifting layers that they are discovered, sometimes 

 with sea- shells, sometimes with the shells of fresh water, but never in 

 the regular stony beds. All that is found with these species is either 

 unknown as they are, or at least doubtful. 



In fact, the bones of the species which appear the same as ours 

 onlv present themselves in the last deposites of alluvions formed on 

 the banks of rivers, or on the beds of old ponds or dried marshes, or in 

 the depths of turf layers, or in the clefts and hollows of certain rocks, 

 or, finallv, at a short distance from the surface, in places where they 

 mav have been imbedded by casualties or by the hand of man ; and 

 their superficial position makes these bones, the most recent of any, 

 almost always in the worst state of preservation. It must not, how- 

 ever, be supposed that this classifying of different relative situations is 

 as clear as that of the species, or that it can have a demonstrative 

 character equally distinct; there are manifest causes why it cannot 

 be so.. 



First, all my arrangements of species have been made on the bones 

 themselves, or on good figures ; it was necessary, on the other hand, 

 that I should have observed myself all the places where these bones 

 have been discovered. Very often I have been compelled to have re- 

 course to vague and ambiguous resemblances, made by persons who 

 did not know what peculiar observations were necessary ; and more 

 frequently still, I have not found any hints at all. 



"Secondly, there must be in this respect infinitely more doubt than with 

 regard to the bones themselves. The same deposite may appear recent 

 in places where it is superficial, and ancient in those where it is covered 

 over by banks which have succeeded it. Ancient layers may have 

 been transported by partial inundations, and have covered recent bones ; 

 they may have been buried beneath them, and have enveloped and 

 mingled with the productions of the ancient seas which they before 

 contained : ancient bones may have been washed by the waters, and 



