FOREIGN CORRESPONDENCE. 



105 



M. Elie de Beaumont, on presenting this letter to the Academy, ob- 

 served that the persevering researches of Professor Sismonda cannot be 

 too highly praised. Having lately visited the Col d'Encombres himself, 

 he gave an interesting account of his recent excursion there, and ex- 

 plained the position and structure of the beds indicated by IT. Sismonda. 

 These vary from 7 j to 10 or 11 feet in thickness ; they are covered by 

 about 100 feet of calcareous strata, apparently devoid of fossil remains, 

 and repose on a bed of grey crystalline limestone, presenting a few veins 

 and blocks of black silica, which emits a bituminous odour when 

 broken. It is very difficult to extract the fossils from these deposits, 

 so firmly are they cemented together by the crystalline limestone. These 

 beds of limestone have, however, completely escaped the metamorphic 

 action which has so thoroughly modified the mineralogical characters 

 of the surrounding strata. Erom this fact, and from the circumstance 

 already mentioned of all the fossils of these three Liassic divisions being 

 here distributed in one single bed, M. Elie de Beaumont is of opinion 

 that the fossil beds of the Col d'Encombres will in future be regarded 

 as one of the most classical and remarkable of the Liassic formations. 



The second letter addressed to the learned Secretary of the Academy 

 was from M. Riviere, who is studying, in Prussia, the direction of 

 the veins of zinc and lead ores. A short paper enclosed in it, 

 and entitled, " On the general direction of the veins of Blende and 

 Galena,'' contains the following results : On the right side of the 

 Rhine, as the author has previously shown, the general direction 

 of these veins (which are encased in the Grauwacke and Phyllades"^' 

 of the country) is east 30 north, west 30° south. Towards 

 the latter part of last year he found that the veins on the left 

 side of the river not only show a similar nature and structure, but 

 appear to have the same direction, as those on the right side ; of which, 

 in fact, they seem to be a prolongation. M. Riviere has also studied 

 the same metallic veins in La Yendee, Auvergne, Eorez, Ardeche, 

 Cevennes, the Alps, &c., and now arrives at these conclusions : first, 

 that there is a remarkable constancy in the mean direction taken by the 

 veins of Blende and Galena throughout a great part of Erance ; secondly, 

 that these veins run generally north-west and south-east, inclining rather 

 to the west and to the east, and seeming to appertain to M. Elie de 

 Beaumont's Systhne du Morlihan, which he has defined by a line to the 



* Clay -slate.— Ed. 



