334 Analysis of the Labours of the Royal Ac'adewy 



of which they present themselves, the author compares them in 

 point of composition and situation with transition rocks, and 

 proves that tliey ought not to be ranked in that class. 



The primitive masses themselves are not always easy Co cha- 

 racterize : the irref^ularity of their position, the vastncss of the 

 spaces through which it is sometin^.es necessary to trace their 

 relations, and the confounding varieties in their composition, 

 present great difficulties. M. Brocliant has furnished us with 

 a striking instance of the mistakes which may be thus occasioned. 

 After long journevs and laborious examinations, he has discovered 

 that the loftv summits of the Alps, from Mount-Cenis even to 

 St. Gothard, and particularly Mont-Blanc, do not consist, as has 

 been believed, of granite p'-operly so called ; but of a variety more 

 crystalhne, and njore abundant of a talcous and feldsparic rock, 

 which often contahis beds of metallic minerals. He has satisfied 

 himself at the same time that real granite pervades the southern 

 border of the chain ; and, reasoning from analogy, he considers 

 it very probable that the granitic stratum supports tlie talcous ; 

 whence he concludes that the higher summits of tlie Alps are" 

 not relativelv thenio.^t ancient part of these mountains. 



It ought always to be remarked, that the primordiality of 

 granite among known rocks is subject to exceptions. M. de 

 Buch has ascertained, in Norway, that granites evidently recog- 

 nisable as such are deposited above strata believed to be of a 

 more modern class, and even strata containing petrifactions. 

 Tiie same thing has been observed in Saxony, and even in Cau- 

 casus. 



M. de Bonnard — who has had the honour of giving to geology 

 the first complete description of the Ertzgeturge — of that pro- 

 vince of Saxonv which is in a manner the country of geology — 

 has endeavoured in that work to determine those places where 

 granite is inferior, and those where it is superior to other strata. 

 It cannot be doubted, after the researches he has made, that the 

 granite of Dohna cannot be in this last situation, as the Saxon 

 geologists have announced ; but in other places, and especially 

 near Freyberg, there ie every reason to believe in the superiority 

 of the granite. It further appears from his observations, that 

 the chain which separates Saxony from Bohemia is distinguished 

 by also having granite on one side, and that the southern. 



The work of M. ,le Bonnard contains many other valuable de- 

 tails upon the nature and position of the strata of this celebrated 

 province, and also on the rich metallic veins which everywhere 

 traverse it, and on which the industry of the people has been so 

 long exercised. In these respects it is equally interesting to geo- 

 logy and to the art of mining. 



M. Heron de Villefosse ha« also rendered to the same art a 



very 



