GEOLOGICAL CHANGE, AND TIME. 121 



eval condition and subsequent histoiy of the planet might be consid- 

 ered from tlie side of astronomy and physics. And it was by investi- 

 gations of this nature that the geological torpor was ev-entually dissi- 

 ]iated. To our illustrious former president, Lord Kelvin, who occupied 

 this chair when the association last met in Edinburgh, is mainly due 

 the rousing of attention to this subject. l>y the most convincing argu- 

 ments he showed how impossible it was to believe in the extreme doc- 

 trine of uniformitarianism. And though, owing to uncertainty in re- 

 gard to some of the data, wide limits of time were postulated by him, 

 he insisted that within these limits the whole evolution of the earth 

 and its inhabitants must have been comi)rised. While therefore the 

 geological doctrine that the present order of Nature must be our guide 

 to the interpretation of the past reumined as true and fruitful as ever, 

 it had now to be widened by the reception of evidence furnished by a 

 study of the earth as a planetary body. The secular loss of heat, 

 which demonstrably takes place both fiom the earth and the sun, made 

 it quite certain that the present could not have been the original con- 

 dition of the system. This diminution of temperature with all its con- 

 sequences is not a mere matter of si)eeulation, but a physical fact of 

 the present time as much as any of the familiar physical agencies 

 that affect the surface of the globe. It points with unmistakable di- 

 rectness to that beginning of things of which Hutton and his followers 

 could lind no sign. 



Another modification or enlargement of the uniformitarian doctrine 

 was lirought about by continued investigation of the tei'restrial crust and 

 consequent increase of knowledge respecting the history of the earth. 

 Though llutton and Playfair believed in periodical catastropiies, and 

 indeed re(]uired these to recur in order to renew and preserve the habit- 

 able condition of our planet, their successors gradually came to view 

 with rei)ngnauee any appeal to abnormal, and especially to violent 

 manifestations of terrestrial vigor, and even persuaded themselves that 

 such slow and comparatively feeble action as had been witnessed by 

 man could iil(»ne be recognized in the evidence from which geological 

 history must be eomi)iled. Well do 1 remember in my own boyhood 

 what a cardinal article of faith this pi-epossessiou had become. \\c 

 were taught by our great and honored master, Lyt^ll, to believe im- 

 plicitly in gentle and unilbrm operations, extended over indetlnite 

 [)eriods of time, though i)ossil»ly some, with the zeal of i)ar(isans, car- 

 ried this belief to an extreme which Lyell himself did not ai)prove. 

 The most stu])end(ms marks of tm'restrial dislurbance, siu-li as the 

 structure of great mountain chains, were deemed to be more sjitisfac- 

 torily accounted for by slow movements prolonged through indefinite 

 ages than by any sudden convulsion. 



What the more extreme members of the uniformitarian school failed 

 to ])erceive was the absence of all evidence that terrestrial catastrophes 

 even on a colossal scale might not be a part of the present economy of 



