Ch. XVII.] 
LACUSTRINE STRATA AUVERGNE. 
229 
Occasionally, when the grits rest on granite, as at Chama- 
lieres before mentioned, and many other places, the separate 
crystals of quartz, mica, and felspar, of the disintegrated 
granite, are bound together again by the silex, so that the 
granite seems regenerated in a new and even more solid form, 
and thus so gradual a passage may sometimes be traced be- 
tween a crystalline rock and one of mechanical origin, that we 
can scarcely distinguish where one ends and the other begins. 
In the Puy de Jussat, and the neighbouring hill of La 
Roche, are white quartzose grits, cemented into a sandstone 
by calcareous matter, which is sometimes so abundant as to 
form imbedded nodules. These sometimes constitute sphe- 
roidal concretions six feet in diameter, and pass into beds of 
solid limestone resembling the Italian travertins, or the de- 
posits of mineral springs. 
In the hills above mentioned, we have the advantage of see- 
ing a section continuously exposed for about 700 feet in thick- 
ness. At the bottom are foliated marls, white and green, 
about 400 feet thick, and above, resting on the marls, are the 
quartzose grits before mentioned with the associated travertins. 
This section is observed close to the confines of the basin, so 
that the lake must here have been filled up near the shore with 
fine mud, before the coarse superincumbent sand was intro- 
duced. There are other cases where sand is seen below the 
marl. 
2. Red marl and sandstone, — But the most remarkable of the 
arenaceous groups is a red sandstone and red marl, identical in 
all their characters with the secondary new red sandstone and 
marl of England. In the latter, the red ground is sometimes 
variegated with light greenish spots, and the same may be seen 
in its tertiary counterpart of fresh-water origin at Coudes, on 
the Allier. The marls are sometimes of a purplish-red colour, 
as at Champheix, and are accompanied by a reddish limestone, 
like the well-known « cornstone,' which is associated with the 
old red sandstone of English geologists. The red sandstone 
and marl of Auvergne have evidently been derived from the 
