236 
EOCENE PERIOD. 
[Cb. XVII. 
grit, sometimes granitiform, reddish and mottled sands and 
conglomerates, all evidently derived from the degradation 
of granitic rocks, and resembling exceedingly the arenaceous 
group of the Limagne before described. This formation is 
almost confined to the borders of the basin, and was evidently 
a littoral deposit. The other member of the formation, the 
marls, are more or less calcareous, and are associated with lime- 
stone and gypsum, which last is worked for agricultural uses, 
and exactly resembles that of Paris. 
The analogy in the mineral character of the Velay and Paris 
basins is rendered more complete by the presence in both of 
silex in regular beds. In the limestone I found gyrogonites, 
or seeds of the Chara, of the same species as those most com- 
mon in the Paris basin ; and M. Bertrand de Doue has dis- 
covered the bones of several mammiferous animals of the same 
genera as those which characterize the basins of Auvergne and 
Paris *. The shells also of this formation correspond specifi- 
cally with those of Eocene formations in other parts of France. 
The sand and. conglomerate of the fresh-water basin of 
Velay is entirely free from volcanic pebbles, agreeing in this 
respect with the analogous group of the Limagne ; but the 
fact is the more striking in Velay, because the masses of tra- 
chyte, clinkstone, and other igneous rock now abounding in 
that country, have an aspect of extremely high antiquity, and 
constitute a most prominent feature in the geological structure 
of the district. Yet the non-intermixture of volcanic pro- 
ducts with the lacustrine sediment, is just what we should 
expect when we have ascertained that the imbedded organic 
remains of those strata are Eocene ; whereas the lavas belong 
in part, if not entirely, to the Miocene period f . 
Cantal. — Near Aurillac, in Cantal, another series of fresh- 
water strata occurs, which resembles, in mineral character and 
organic remains, those of Auvergne and Velay already de- 
scribed. The leading feature of this group, as distinguished 
* Descrip. Geognos. des Env. du Puy en Velay, 1823. 
f l-see above, p, 219, and below, Chap. xix. 
