File:The Quarterly journal of the Geological Society of London (12645008385).jpg

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-