338 AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 



years ago. If it were absolutly impossible to find out wliicli of these 

 periods is more probable than the other, then I agree we might be Gral- 

 lios as to the date of the Norman Conquest. But a 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 of this subject, in various largely used 

 popular text-books, and in scientific writings which were new in 1868, 

 or not too old 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, 



page 287 : 



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

 elapsed siuce the latter part of the 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 pro- 

 duced a revolution in natural science, yet does not admit how incom- 

 prehensihly vast have been the vast 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 tvliicJi we can 

 set no hoimds in the ])ast^ 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, thowg\i it must be confessed that many 

 problems in geology seem to find their solution only through the ad- 

 mission 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, page 82, says : 



" The infinite time of the geologists ife in the past 5 and most of their 

 speculations regarding this subject seem to imply the absolute infinity of 

 /me, 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, 



