84 CRETACEOUS GROUP &C. 
other words, that they were contemporaneous beings. 
Whatever cause laid bare the eastern portion of the se- 
ries, appears to have acted simultaneously on the western 
mass: not a rush of currents, but either a subsidence of 
the sea, or elevation of the land, which has left the fossils 
in their original beds unbroken, and, as to their external 
form, unaltered. 
In conclusion, I beg leave to state, that this work has 
been written during the constant interruptions of a pro- 
fessional life ; and I cast it as a grain of sand on the moun- 
tain of geological knowledge, which has been heaped up 
by the genius and industry of the naturalists of both he- 
mispheres. 

