74 THE CANADIAN NATURALIST. [March 



interesting calculations, not only bearing on these questions, but 

 also on the entire age of the earth, and on the relative duration 

 of geological periods. Of course in such inquiries much is 

 conjectural, and the most precise calculations may be vitiated by 

 uncertainties as to the data. Still anything having even the 

 aspect of arithmetical results is preferable to the vague assump- 

 tion of indefinite periods, and may at length lead to reliable 

 conclusions. In the meantime we give the following as an 

 illustration of the manner in which Mr. Croll deals with the 

 subject : — 



"But is it the case that geology really requires such enormous 

 periods as is generally supposed ? At present, geological esti- 

 mates of time are little else than mere conjectures. Greological 

 science has hitherto afforded no trustworthy means of estimating 

 the positive length of geological epochs. Geological phenomena 

 tell us most emphatically that these periods must be long ; but 

 how long, these phenomena have, as yet, failed to inform us. 

 Geological phenomena represent time to the mind under a most 

 striking and imposing form. They present to the eye, as it were, 

 a sensuous representation of time ; the mind thus becomes deeply 

 impressed with a sense of immense duration ; and when one 

 under these feelings is called upon to put down in figures what 

 he believes will represent that duration, he is very apt to be de- 

 ceived. If, for example, a million of years as represented by 

 geological phenomena and a million of years as represented by 

 figures were placed before our eyes, we should certainly feel 

 startled. We should probably feel that a unit with six ciphers 

 after it was really something far more formidable than we had 

 hitherto supposed it to be. Could we stand upon the edge of a 

 gorge a mile and a half in depth that has been cut out of the 

 solid rock by a tiny stream, scarcely visible at the bottom of this 

 fearful abyss, and were we informed that this little streamlet was 

 able to wear off annually only to of an inch from its rocky bed, 

 what would our conceptions be of the prodigious length of time 

 that this stream must have taken to excavate the gorge ? We 

 should certainly feel startled when, on making the necessary cal- 

 culations, we found that the stream had performed this enor- 

 mous amount of work in something les,^ than a million of 

 years. 



If we could possibly form some adequate conception of a 

 period so prodigious as one hundred millions of years, we should 



