﻿Vol. 64.] ANNIVEESAET ABDEESS OF THE PEESIDENT. CVii 



subordinate and comparatively neglected branch of geology, it may 

 DOW claim the dignity of an almost independent science. In 

 contemplating this revolution — undoubtedly the most momentous of 

 the last fifty years in any department of geological science — w^e of 

 the Geological Society of London may be pardoned if, with a feeling 

 of pride, we remember that it was started and received its earliest 

 impulse within our walls at the hands of one of our Fellows who is 

 happily still with us, and still in his old age communicates the results 

 of his continued researches.^ Ko pages in the volumes of our 

 Quarterly Journal have been so fecund as those which announced 

 to the world the advent of this new era in the investigation of the 

 materials of the crust of the earth. In the eight years which 

 followed 1850 Mr. Henry Clifton Sorby communicated to the 

 Society a series of papers,^ in which he showed how by adopting the 

 method of preparing thin transparent slices of mineral substances, 

 a process which had been devised before the year 1831 by William 

 Nicol,^ of Edinburgh, the minutest structures of rocks could be 

 revealed and examined. He began by describing the constitution of 

 the Calcareous Grit of Yorkshire and various limestones. Gaining 

 courage with experience, he realized the endless capabilities of this 

 method of petrographical analysis, and soon boldly attacked various 

 metamorphic and igneous rocks. He showed how it was now 

 possible to investigate with precision the mineral constitution of 

 rocks, to determine their microscopic structure, to ascertain the 

 probable conditions and depths at which they consolidated, and to 

 trace the subsequent changes which they have undergone. 



This epoch-marking demonstration of the fruitfulness of the 

 application of the microscope to the elucidation of the composition 

 and genesis of rocks was published in the Quarterly Journal for 

 1858. Its appearance might have been supposed certain at 



^ As these pages are passing through the press the news has reached me 

 that our veteran colleague has passed away. Though confined to bed, he had 

 retained his mental faculties unimpaired. Only a fortnight before his death 

 I received a letter from him in his own clear handwriting, in which he enquired 

 after the disposition of specimens which he had studied half a century ago. 



2 Q. J. vii, 1 ; ix, 344 ; x, 328 ; xii, 137 ; xiv, 453. See also his Presidential 

 Addresses in vols, xxxv & xxxvi (1879-80). 



^ Nicol's invention consisted in polishing thin pieces of stone, fixing them on 

 glass with Canada balsam, and reducing them in thickness until they became 

 transparent. It was applied by him to the elucidation of the structure of 

 fossil wood, and the first account of it was prepared by him for Henry 

 Witham's * History of Fossil Vegetables,' published in 1831. 



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