HIS GEOLOGICAL ZEAL 247 



watch for new facts in many fields of natural know- 

 ledge, it is to the geological problems that he returns 

 most frequently and fully. And never before in the 

 history of science had these problems been attacked 

 by an actual observer over so vast a space of the earth's 

 surface, with more acuteness and patience, or discussed 

 with such breadth of view. There is something almost 

 ludicrous in the contrast between his method of treat- 

 ment of volcanic phenomena and that of his professor 

 at Edinburgh only six short years before. But though 

 geological questions, being the most obvious and 

 approachable, took up so large a share of his time 

 and attention, he was already pondering on some of 

 the great biological mysteries the unveiling of which 

 in later years was to be his main occupation, and to 

 form the basis on which his renown as an investigator 

 was chiefly to rest. 



On his return to England, in October 1836, Darwin 

 at once took his place among the acknowledged men of 

 science of his country. For a time his health continued 

 to be such as to allow him to get through a large 

 amount of work. The next two years, which in his 

 own opinion were the most active of his life, were 

 spent, partly at Cambridge and partly in London, in 

 the preparation 'of his Journal of Researches, of the 

 zoological and geological results of the voyage, and 

 of various papers for the Geological and Zoological 

 Societies. So keen was his geological zeal that, almost 

 against his better judgment, he was prevailed upon to 

 undertake the duties of honorary secretary of the Geo- 

 logical Society, an office which he continued to hold 

 for three years. And at each period of enforced 



