2(J ON THE REVOLUTIONS OF 



sea into islands by projecting chains, there must have been various-' 

 changes in many particular basins. 



We must perceive, that, in the midst of such changes in the nature 

 of the liquid, the animals which it nourished could not remain the 

 same. The species, their very genus, changed with the layers ; and, 

 although at short intervals we may meet with a recurrence of similar 

 species, it is correct to say, in a general sense, that the shells of the 

 ancient layers have their peculiar shapes, which are gradually lost, 

 and not found again in recent layers, still less in the sea itself, where 

 we never detect analogous species, nor are many of the species itself 

 found ; that the shells of recent layers, on the contrary, resemble in 

 genus those still to be found in our seas, and that in the most recent 

 and most shifting of these layers, and in certain lakes and more 

 limited deposits, there are some species which the most practised eye 

 cannot distinguish from those to be found on neighbouring coasts. 



There has then been in animal nature a succession of changes which 

 has been occasioned by those of the liquid in which the animals lived, 

 or which at least have had relation to them, and these variations have 

 gradually brought the classes of aquatic animals to their present state ; 

 in fact, when the sea finally quitted the continents its inhabitants 

 differed but very little from those which it now produces. 



We say, finally quitted, because if we scrutinize with the most 

 exact care these relics of organic beings, and discover amidst marine 

 layers, even the most ancient, layers composed of animal or vegetable 

 productions of the earth and soft water, and amongst the most recent 

 layers, that is, the most superficial, we shall find those in which 

 terrestrial animals are buried beneath masses of marine productions. 

 Thus the various catastrophes which have shaken the layers have not 

 only produced by degrees from the bosom of the waters the different 

 portions of our continents, and lessened the basin of the sea ; but the 

 basin has been displaced in many ways. It has often happened that 

 lands left dry by the retiring of the waters have been again overflowed 

 by that element, whether they have been cast down, or the waters 

 have only flowed over them j and as to the soil left dry by the sea at 

 its last retreat, which man and terrestrial animals now inhabit, it had 

 been already left dry once before, and then nourished quadrupeds, 

 birds, plants, and every kind of terrestrial productions ; the sea which 

 has left it had formerly covered it. The changes in the height of the 

 waters have not arisen solely from a retiring, more or less gradual or 

 general ; it has proceeded from divers overflowings and divers retir- 

 ings, the final result of which has been an universal sinking of the 

 level. 



