Earth as an Abode fitted for Life. 67 



change took place just about the time to which I refer, and 

 from then till now geologists have not considered the question 

 of absolute dates in their science as outside the scope of their 

 investigations. 



§ 3. I may be allowed to read a few extracts to indicate 

 how geological thought was expressed in respect to this 

 subject, in various largely used popular text-books, and in 

 scientific writings which were new in 1868, or not so old as 

 to be forgotten. I have several short extracts to read and 

 I hope you will not find them tedious. 



The first is three lines from Darwin's " Origin of Species," 

 1859 Edition, p. 287. 



" In all probability a far longer period than 300,000,000 years has 

 elapsed since the latter part of tlie secondary period." 



Here is another still more important sentence, which I read 

 to you from the same book : — 



" He who can read Sir Charles Lyell's grand work on the Principles 

 of Geology, which the future historian will recognize as having produced 

 a revolution in natural science, yet does not admit how incomprehensibly 

 vast have been the past periods of time, may at once close this volume" 



1 shall next read a short statement from Page's ' Advanced 

 Students' Text-Book of Geology,' published in 1859 : — 



" Again where the FORCE seems unequal to the result, the student 

 should never lose sight of the element TIME : an element to ivhich we can 

 set no bounds in the past, any more than we know of its limit in the 

 future." _ 



" It will be seen from this hasty indication that there are two great 

 schools of geological causation -the one ascribing every result to the 

 ordinary operations of Nature, combined with the element of unlimited 

 time, the other appealing to agents that operated during the earlier 

 epochs of the world with greater intensity, and also for the most part 

 over wider areas. The former belief is certainly more in accordance with 

 the spirit of right philosophy, though it must be confessed that many 

 problems in geology seem to find their solution only through the 

 admission of the latter hypothesis." 



§ 4. I have several other statements which I think you may 

 hear with some interest. Dr. Samuel Haughton, of Trinity 

 College, Dublin, in his ' Manual of Geology/ published in 

 1865, p. 82, says :• — 



"The infinite time of the geologists is in the past ; and most of their 

 speculations regarding this subject seem to imply the absolute infinity of 

 time, as if the human imagination was unable to grasp the period of time 

 requisite for the formation of a few inches of sand or feet of mud, and its 

 subsequent consolidation into rock." (This delicate satire is certainly 

 not overstrained.) 



" Professor Thomson has made an attempt to calculate the length of 

 time during which the sun can have gone on burning at the present rate, 

 and has come to the following conclusion : — ' It seems, on the whole, most 



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