666 



SCIENGK 



[N. S. Vol. IX. No. 228. 



earth essentially depends, is because he did 

 not know that there was valid foundation 

 for any estimates worth considering as to 

 absolute magnitudes. If science did not al- 

 low us to give any estimate whatever as to 

 whether 10,000,000 or 10,000,000,000 years 

 is the age of this earth as an abode fitted 

 for life, then I think Professor Huxley 

 would have been perfectly right in saying 

 that geologists should not trouble them- 

 selves about it, and biologists should go on 

 in their own way, not inquiring into things 

 utterly beyond the power of human under- 

 standing and scientific investigation. This 

 would have left geology mvich in the same 

 position as that in which English history 

 would be if it were impossible to ascertain 

 whether the battle of Hastings took place 

 800 years ago, or 800 thousand years ago, 

 or 800 million years ago. If it were ab- 

 solutely impossible to find out which of 

 these periods is more probable than the 

 other, then I agree we might be Gallios 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 geol- 

 ogists 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 ex- 

 tracts 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 jmrt of the 

 secondary period." 



Here is another still more important sen- 

 tence, 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 his- 

 torian will recognize as having produced a revolution 

 in natural science, yet does not admit how incompre- 

 hensibly vast have been the past periods of time, maif 

 at once close this volume." 



I shall next read a short statement from 

 Page's ' Advanced Students' Text- Book 

 of Geology,' published in 1859 : 



"Again, where the FOECE seems unequal to the re- 

 sult the student should never lose sight of the ele- 

 ment TIME, an element to xohich we can set no bounds in 

 the past, any more than we know of its limit in th& 

 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 opera- 

 tions of Nature, combined with the element of un- 

 limited 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 ac- 

 cordance with the spirit of right philosophy, though it 

 must be confessed that many problems in geology 

 seem to find their solution only through the admis- 

 sion of the latter hypothesis." 



§ 4. I have several other statements 

 which I think you may hear with some in- 

 terest. Dr. Samuel Haughton, of Trinity 

 College, Dublin, in his ' Manual of Geol- 

 ogy,' published in 1865, p. 82, says : 



" The infinite time of the geologists is in the past; 

 and ntost 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 

 rook." (This delicate satire is certainly not over- 

 strained. ) 



" Professor Thomson has made an attempt to cal- 

 culate 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 probable that the sun has not illu- 

 minated the earth for 100,000,000 years, and almost 

 certain that he has not done so for 500,000,000 years. 

 As for the future, we may say with equal certainty, 

 that the inhabitants of the earth cannot continue to- 

 enjoy the light and heat essential to their life for 

 many million years longer, unless new sources, now 



