INCONCEIVABLE LAPSE OF TIME. 337 
calculated by thousands of years, but by paleontological 
or geological periods, each of which comprises many thou- 
sands of years, and perhaps millions, or even milliards, 
of thousands of years. It is of little importance how high 
the immeasurable length of these periods may be approxi- 
mately estimated, because we are in fact unable with our 
limited power of imagination to form a true conception of 
these periods, and because we do not as in astronomy 
possess a secure mathematical basis for fixing the approxi- 
mate length of duration in numbers. But we most positively 
deny that we see any objection to the theory of develop- 
ment in the extreme length of these periods which are so 
completely beyond the power of our imagination. It is, on 
the contrary, as I have already explained in one of the 
preceding chapters, most advisable, from a strictly philoso- 
phical point of view, to conceive these periods of creation 
to be as long as possible, and we are by so much the less 
in danger of losing ourselves in improbable hypotheses, 
the longer we conceive the periods for organic processes 
of development to have been. The longer, for example, we 
conceive the Permian period to have been, the easier it 
will be for us to understand how the important transmuta- 
tions took place within it which so essentially distinguish 
the fauna and flora of the Coal pericd from that of the 
Trias. The great disinclination which most persons have to 
assume such immeasurable periods, arises mainly from the 
fact of our having in early youth been brought up in the 
notion that the whole earth is only some thousands of 
years old. Moreover, human life, which at most attains 
the leneth of a century, is an extremely short space of 
time, and is not suitable as a standard for the measure- 
