Pf^OJ?£- IN- PALEONTOLOGY 147 



delicate parts, their sharpest ridges, and their finest 

 and tenderest processes." 



" We are therefore forcibly led to believe not only 

 that the sea has at one period or another covered all 

 our plains, but that it must have remained there for 

 a long time and in a state of tranquillity, which cir- 

 cumstance was necessary for the formation of deposits 

 so extensive, so thick, in part so solid, and filled with- 

 the exuviae of aquatic animals." 



But the traces of revolutions become still more 

 marked when we ascend a little higher and approach 

 nearer to the foot of the great mountain chains. 

 Hence the strata are variously inclined, and at times 

 vertical, contain shells differing specifically from those 

 of beds on the plains below, and are covered by hori- 

 zontal later beds. Thus the sea, previous to the 

 formation of the horizontal strata, had formed others, 

 which by some means have been broken, lifted up, 

 and overturned in a thousand ways. There had 

 therefore been also at least one change in the basin 

 of that sea which preceded ours ; it had also experi- 

 enced at least one revolution. 



He then gives proofs that such revolutions have 

 been numerous. 



"Thus the great catastrophes which have 7 ~ 

 duced revolutions in the basins of the sea we^c p. 

 ceded, accompanied, and followed by changes in the 

 nature of the fluid and of the substances which it 

 held in solution, and when the surface of the seas 

 came to be divided by islands and projecting ridges, 

 different changes took place in every separate basin," 



