Vol. 65.] ANNIVERSARY ADDRESS OE THE PRESIDENT. li 



Looking back towards the close of his life, Sorby regarded his 

 early training with complete approval : he had found it ' of the 

 greatest possible value' in all the investigations he had undertaken. 

 It says much for his natural gifts that he was able to dispense with 

 the discipline of examinations, and that the special qualities of 

 exactitude and completeness which it fosters are none the less 

 distinctive characteristics of all his work. 



The happy possessor of a private fortune, Sorby was able to 

 devote himself unreservedly to the work of discovery, which 

 engaged all his energies from his first paper, written in his 20th 

 year, to the last day of his life at the ripe age of 81. 



The earliest essays of original genius are often surprisingly 

 commonplace. Faraday's first contribution to science was the 

 analysis of a piece of lime ; Sorby's, a collection of analyses which 

 he had made in order to determine the amount of sulphur and 

 phosphorus present in various kinds of agricultural crops. 



Very soon, however, he plumed his pinions to wider flights. 

 Fundamental problems in geology, especially such as are connected 

 with the deposition of sediments, early engaged his attention and 

 continued to occupy his thoughts throughout his life : his latest as 

 well as many of his earlier papers are devoted to this subject, and 

 he expressed his surprise, which every thoughtful geologist must 

 share, that it has not received more general investigation. But 

 Sorby's first great achievement was the application of the micro- 

 scope to the study of rocks. The process of preparing thin sections 

 of hard bodies for examination under the microscope had been 

 practised since the time of Nicol, who was, I believe, its inventor ; 

 Sorby learnt it from William Crawford Williamson of Manchester, 

 and was fascinated by a method which opened a way into the 

 unseen. 



The first transparent slice of a rock was made by him in 1849, 

 and the first petrographical study based on thin slices was an 

 account of the minute structure of the calcareous grit of Scar- 

 borough, read before this Society in 1850 and published in our 

 Journal in 1851. Almost all the methods commonly employed at 

 the present day in the microscopical study of rocks, including the 

 application of polarized light, were already familiar to Sorby at this 

 early date. 



The powers of the new method were next to be felt in a still 

 more difficult field of enquiry. Daniel Sharpe had shown by an 

 excellent piece of inductive reasoning that slaty cleavage was a 



