INCONCEIVABLE LAPSE OF TIME. 337 



calculated by thousands of years, but by palseontological 

 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 period 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 length of a century, is an extremely short space of 

 time, and is not suitable as a standard for the measure- 

 jf VOL. n. z 



