GEOLOGICAL RELATION. 185 
tainty of a science, but it is from time to time amply 
repaying the benefit, by making known the condition of 
the animal kingdom at remote periods of time. We 
are thus enabled to obtain glimpses of the state of the 
earth when races of animals very different from those 
now living inhabited it, and to note their successive ap- 
pearances and decline, until at length we reach the time 
when animals which are still extant began to prevail. 
The results afforded by such observations are among the 
most wonderful presented to us by science. They tend 
to enlarge our ideas of the power of the Creator, while 
they multiply infinitely our conceptions of the unlimited 
variety of created things, and of the immeasurable du- 
ration of their existence. 
Guided by the light reflected from geological sci- 
ence, w r e may feel rationally authorized to draw from 
the preceding facts and considerations the following 
inferences. That our existing species of land mollusks 
were living at a period which, though recent in a geo- 
logical sense, was anterior to the last geological revolu- 
tion, when the surface of this portion of the earth was 
brought to its present condition, and to the existence of 
the higher orders of animals which now inhabit it, and 
even to that of the extinct mammalians which are known 
only by their gigantic remains. That, during the period 
of the deposition of the newest tertiary beds they 
were at least as numerous as at present, and that conse- 
quently, the existing epoch cannot be considered as that 
of their greatest development. That, in the interval of 
vol. i. 48 
