1848.] MURCHISON ON THE STRUCTURE OF THE ALPS. 



181 



Buch pointed out to me the clear determination of the Oxfordian 

 formation by the presence of several of the fossils above enumerated ; 

 and in the grand natural sections between Rovereto and the Corneto 

 pass, I also perceived a fine succession under the Ammonitico rosso. 



The same Oxfordian zone has been delineated in Piedmont and 

 Savoy by M. Sismonda. In the environs of Chambery and Aix les 

 Bains, I had the advantage of studying its relation to the superior or 

 cretaceous strata with the Canon Chamousset. That geologist has 

 there divided the great Oxfordian masses into four parts, the lowest 

 of which are marly limestones in beds of about a foot thick. 2ndly, 

 Limestones, deep grey or bluish, with white veins and some ferrugi- 

 nous oolite. It is this band which contains most of the fossils, inclu- 

 ding the Ammonites biplex, &c., with Aptychi, &c. 3rdly, Foliated 

 marls or calcareous flags ; and, 4thly, Marly limestone, &c. This 

 zone is overlaid by limestone with many corals, which is paralleled 

 with the coral rag of English geologists, and that again is conformably 

 overlaid by a full expanse of the neocomian formation, which in this 

 region is divisible into three parts. 



Not describing all these strata, I here merely annex a general sec- 

 tion from the base of the Oxfordian to the summit of the Neocomian, 

 which I made on the western shore of the Lac de Bourget on 

 the sides of the zigzag road from Chambery to Lyons, which tra- 

 verses the Montague du Chatf . This Oxfordian group forms the 



w. 



Fig. 3. 



Mt. du Chat. 



Lake of 

 Bourget. 



Cretaceous. 



Upper Neocomian limestone with Chama ammonia. 



Middle Neocomian with Spatangus retusus. 



Lower Neocomian, greenish ferruginous calc grit with Ostrece, Pectens, &c. 



base of EngUsh Lower greensand. 

 Coralline limestone = Coral rag. Summits dolomitic. 

 Oxfordian Jura with Kelloway rock fossils. 2. Schists and limestones. 



f 3 

 Jurassic. < ' 



base of all the outer edges of the Savoy Alps ; their summits usually 

 consisting of neocomian limestone, and often covered by still younger 

 rocks. This order is seen around Chambery and the lake of Bourget 

 at Annecy, in the valley of the Arve, both above and below Sallenches, 

 and near Geneva. 



The Oxfordian limestones, but without such a capping, are co- 

 piously exhibited in the range of mountains east of Vevey. At 

 Chatel St. Denis, where the limestone is very mottled and con- 

 cretionary, it is loaded with ammonites and Aptychi | ; and the same 

 rock, subjected to great flexures, rises into the high peak, the Dent 



t See Bull. Geol. Soc. Fr. new ser. t.i. pi. 9. fig. 3. 



X I was directed to these limestones by M. Studer, and M. Collon of Vevey ac- 

 companied me thither. 



