456 Notices of Memoirs — British Association — 



the firmament also no mark could be discovered of the commence- 

 ment or termination of the present order, no symptom of infancy or 

 old age, nor any sign by which the future or past duration of the 

 universe might be estimated.^ He thus advanced beyond the strictly 

 geological bases of reasonings and committed himself to statements 

 which, like some made also by Hutton, seem to have been suggested 

 by certain deductions of the French mathematicians of his day 

 regarding the stability of the planetary motions. His statements 

 have been disproved by modern physics ; distinct evidence, both 

 from the earth and the cosmos, has been brouglit forward of 

 progress from a beginning which can be conceived, through successive 

 stages to an end which can be foreseen. But the disproof leaves 

 Hutton's doctrine about the vastness of geological time exactly where 

 it was. Surely it was no abuse of language to speak of periods as 

 being vast which can only be expressed in millions of years. 



It is easy to understand how the Uniformitarian school, which 

 sprang from the teaching of Hutton and Playfair, came to believe 

 that the whole of eternity was at the disposal of geologists. In 

 popular estimation, as the ancient science of astronomy was that 

 of infinite distance, so the modern study of geology was the 

 science of infinite time. It must be frankly conceded that geologists, 

 believing themselves unfettered by any limits to their chronology, 

 made ample use of their imagined liberty. Many of them, following 

 the lead of Lyell, to whose writings in other respects modern geology 

 owes so deep a debt of gratitude, became utterly reckless in their 

 demands for time, demands which even the requirements of their own 

 science, if they had adequately realized them, did not warrant. The 

 older geologists had not attempted to express their vast periods in 

 terms of years. The indefiniteness of their language fitly denoted 

 the absence of any ascertainable limits to the successive ages with 

 which they had to deal. And until some evidence should be 

 discovered whereby these limits might be fixed and measured 

 by human standards, no reproach could justly be brought against the 

 geological terminology. It was far more philosophical to be content, 

 in the meanwhile, with indeterminate expressions, than from data 

 of the weakest or most speculative kind to attempt to measure 

 geological periods by a chronology of years or centuries. 



In the year 1862 a wholly new light was thrown on the question 

 of the age of our globe and the duration of geological time by the 

 remarkable paper on the Secular Cooling of the Earth communicated 

 by Lord Kelvin (then Sir William 'I'honison) to the Eoyal Society of 

 Edinburgh.^ In this memoir he first developed his now well-known 

 argument from the observed rate of increase of temperature down- 

 wards from the surface of the land. He astonished geologists by 

 announcing to them that some definite limits to the age of our planet 

 might be ascertained, and by declaring his belief that this age must 

 be more than 20 millions, but less than 400 millions of years. 



1 " Illustrations of the Huttonian Theory," § 118. 

 ^ Traus. Eoy. See. Edin., vol. xxiii (L862). 



