Life Changes on the Globe. 333 



period of time, and has now approached so near its ultimate 

 limit, that if the earth's refrigeration should continue under 

 the same natural conditions as at present, it would require, as 

 shown by Poisson, the enormous period of a hundred thousand 

 millions of years to reduce this small fraction to half its actual 

 value We are, however, more immediately con- 

 cerned with past than with future changes. We should not be 

 justified in supposing from what I have stated respecting the 

 slow future variations of the earth's superficial temperature, 

 that it has been equally slow for an equal period of past time ; 

 but it is still highly probable that some millions of centuries 

 must have elapsed since the mean superficial temperature could 

 have been greater by a single degree than at present, from the 

 operation of the causes We are now discussing.'"* Changes in 

 climate within the periods we trace, are to be accounted for as 

 the results of varying configurations of land and water very 

 gradually and slowly produced. They must have been im- 

 portant agencies in modifying the life upon the globe, but if 

 ever the laws regulating the succession of animated beings are 

 to be understood, the explanation must come from biological 

 inquiries ; and until physiology and kindred sciences have 

 entered into their deductive stage, it is not probable that the 

 question of the Origin of Species will be definitively solved. 



As is usually the case with reformers, whatever may be the 

 sphere of their labours, Professor Huxley neither stands alone 

 in the opinions which he has enunciated, nor has he risen 

 abruptly to be the pioneer of a new process of inquiry. As 

 he himself remarked, others had felt similar difficulties, and 

 cherished similar thoughts. He, however, has given clear and 

 distinct utterance to what they hesitated to state, and although 

 we think a few inaccuracies of expression occur in his admi- 

 rable paper, further consideration only deepens the conviction 

 produced upon all who were so fortunate as to hear the address 

 delivered, that it exhibits that rare combination of the faculty 

 of reasoning with ample knowledge of detail, which characterizes 

 a work destined to be a landmark in the search for truth. 



* Quarterly Journal of the Geological Society, February 1852, p. 59. 



