WORK IN PALAAONTOLOGY 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 
along time and ina 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 exuviez 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 hort- 
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 pro- 
duced revolutions in the basins of the sea were pre- 
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.” 
