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266 F O S S I L R EM A I N S .
down, and covered the lower bed of the
river entirely, for about the space of sixty
yards. It is possible to descend and walk,
with some difficulty, over this part, when
the Rhone is low; but in the summer,
during the melting of the Alpine snows,
tlie river is much enlarged, and flows over
it. The hard calcareous rock in which the
Rhone has excavated this deep tunnel,
contains few, if any, fossils ; but the softer
stratum above it contains numerous casts
o f ammonites, belemnites, trochites, &c.
Over this softer stratum is a yellowish calcareous
bed, which is often variegated and
intermixed with argillaceous and ferruginous
earth, in veins and spots. This bed
contains numerous lenticular-shaped fossils,
that were supposed to be numulites, but
which the French naturalists have determined
to be small madrepores, and M. de
Lamark has given them the name of
orhiolites lenticulata. In one part which
I examined, the whole bed appeared to be
composed of these fossils.
The beds above this consist of alternations
of calcareous and argillaceous marl,
with sand intermixed with particles of
green earth. The fossils from these beds
Î
have been recently examined by M. Brog-
niart, and found to be similar to those from
the lowest part of the chalk formation in
France and England ; indeed, some of them
are identically the same. Though the mine-
ralogical characters of these beds, differ in
many respects from those of our chalk-marl,
and green sand, yet the similarity of some of
the fossils, the identity of others, and the
intermixture of green particles, appear to
justify M. Brogniart in classing the upper
beds at the Perte du Rhône, with the lowest
part of the chalk formation in France and
England, which M. Brogniart denominates
Craie cliloritée.
I f the beds at the Perte du Rhône be the
same as those I observed behind Bellegarde,
where the V alteline has excavated a profound
section in the strata, they alternate
with a rock resembling chalk ; at least, they
rest upon it. It can excite no surprise
that the calcareous formations in the Alps,
which are on a scale so greatly exceeding
in magnitude any similar formations in
England, should present alternations which
are no where to be found in our own island,
nor is it contrary to analogy to suppose,
that in some countries chalk or chalk-marl