326 Geological Society :-— 



oxide and alumina, which results in the development of the red 

 colour of the gem, is not effected at low or even moderately high 

 temperatures, but requires a heat as high as that of the oxyhydrogen 

 blowpipe. It is not necessary that the chromium should be pre- 

 sented to the alumina in the form of chromic acid. It appears, 

 therefore, that the red colour of the ruby is not caused by the 

 presence of chromic acid ; it is, in fact, a reaction sui generis be- 

 tween alumina and chromic oxide, which, as far as my experiments 

 have gone, only takes place at very elevated temperatures. 



In my next communication I propose to give the results of a 

 comparative study of two of the processes most generally em- 

 ployed for the analysis of emeralds, beryls, and other minerals 

 containing glucina and alumina — namely, the carbonate-of -ammonia 

 process of Yauquelin, and the caustic-potash method devised by 

 the same chemist, but modified by Ghnelin, and generally associ- 

 ated with his name. These studies are already far advanced. 



Specimens of various beryl glasses, cut and uncut, accompany 

 this paper. 



GEOLOGICAL SOCIETY. 



[Continued from p. 174.] 



January 8, 1873. — 'Prof. Bamsay, E.H.S., Vice-President, 



in the Chair. 



The following communication was read : — 



" The Secondary Rocks of Scotland."— First Paper. By John W. 

 Judd, Esq., E.G.S. 



Introduction. 



The Mesozoic periods are in Scotland represented only by a 

 number of isolated patches of strata situated in the Highlands and 

 Western Isles, which have been preserved from the destructive effects 

 of denudation either through having been let down by great faults 

 among the Palaeozoic rocks, or through being sealed up under vast 

 masses of Tertiary lavas. The Cretaceous rocks, exhibiting very 

 interesting characters and yielding a beautiful series of fossils, were 

 discovered by the author of the paper during the past year on the 

 mainland and in several of the islands of the west of Scotland. The 

 Jurassic rocks, which were first described by Murchison, are now 

 shown to present a remarkable contrast with their equivalents in 

 England, in being constituted, throughout their whole thiclcness, by 

 alternations of marine and estuarine series of beds, in which respect 

 they precisely resemble the equivalent strata of Sweden. The 

 Triassic rocks have now been discovered in Sutherland, where 

 their conformable relations to overlying beds containing a fine 

 Liassic fauna, entirely confirm the conclusions concerning their age 

 derived from Prof. Huxley's studies of the remarkable reptiles 

 yielded by them in Elgin. 



Part I. /Strata of the Eastern Coast. 

 These consist of a number of patches, situated around the shores 



