196 Henry Clifton Sorhy, LL.D., F.R.S., RG.S., etc., 



a slide prepared from what is probably the first transparent microscopic 

 section of a rock ever prepared, and also exhibit another slide from 

 the first drawing of the structure made in 1849." ' He goes onto 

 relate : " My first published paper in connection with the structure 

 of rocks was in relation to an interesting deposit called the Calcareous 

 Grit, below the Castle Rock at Scarborough. I wrote a paper, sent 

 it to the Geological Society, and it was published by the Society in 

 1850. That paper was the first of its type, and it is interesting to 

 refer to it because at that early date I had developed almost all the 

 methods that are employed even up to the present day in studying 

 the microscopic structure of rocks." ("Fifty Years of Scientific 

 Research," p. 5.) 



This early paper seems never to have attracted the attention it 

 deserved. That Sorby's estimate of its importance is not by any 

 means exaggerated will at once appear upon a perusal of it. Sorby 

 separated the constituents of the rock both by mechanical and chemical 

 methods; he determined the proportions of these constituents to one 

 another, measuring their particles down to the o^o u-o o of an inch ; he 

 prepared sections of the rock, little more than toVo of an inch thick, 

 finding it necessary to make some of these sections of large size ; and 

 not only did he employ very high powers of the microscope, but he 

 used polarized light, both parallel and convergent, and showed their 

 use in distinguisliing between calcite, quartz, and chalcedony. 



This little memoir, which was read before the Geological Society on 

 November 6th, 1850, gave, in fact, a remarkable forecast of the methods 

 and modes of reasoning which have brought microscopical petrography 

 to its present position as a branch of geological research. The paper, 

 as published in the Quarterly Journal of the Geological Society 

 (vol. vii, pp. 1-6), was without illustrations, but a plate with some 

 of Sorby's own drawings was published in the Proc. W. Yorks. Geol. 

 Soc, iii (1851), pp. 197-206. 



Sorby continued all through his life this work on the structure of 

 limestones and other sedimentary rocks, being led especially to note the 

 part played by calcite and aragonite, and the wonderful pseudomorphic 

 changes going on in calcareous deposits. To this subject he devoted 

 his two addresses to the Geological Society in 1879 and 1880, and his 

 latest memoir, completed on his deathbed, was a further exposition 

 of the problem. 



But Sorby's studies were not hj any means confined to the calcareous 

 rocks. He informs us that Daniel Sharpe's writings directed him in 

 1851 to the study of slaty cleavage, and of his work in this direction he 

 writes as follows: — " For some time I had been occupied with the study 

 of the microscopical character of rocks possessing slaty cleavage, a 

 problem which had previously attracted much attention, but was still 

 involved in so much obscurity that several theories, all equally unsatis- 

 factory, had been propounded. The more I studied the microscopical 

 structure of these cleaved rocks, the more was I puzzled with the 

 observed facts. One day when quietly walking in my garden and 



1 "We uuderstand that these early sections and cbawings are to be preserved in the 

 City Museum at Sheffield. 



