LOWER MIOCENE OE CENTRAL FRANCE. ^233 
tions. Lastly, these quadrupeds became extinct, and gave 
place in their turn to the species now existing. There are 
no signs, during the whole time required for this series of 
events, of the sea having intervened, nor of any denudation 
which may not have been accomplished by currents in the 
different lakes, or by rivers and floods accompanying repeat¬ 
ed earthquakes, or subterranean movements, during which 
the levels of the district have in some places been material¬ 
ly modified, and perhaps the whole upraised relatively to the 
surrounding parts of France. 
Auvergne ,—The most northern of the fresh-water groups 
is situated in the valley-plain of the Allier, which lies within 
the department of the Puy de Dome, being the tract which 
went formerly by the name of the Limagne- d’Auvergne. 
The average breadth of this tract is about twenty miles; 
and it is for the most part composed of nearly horizontal 
strata of sand, sandstone, calcareous marl, clay, and lime¬ 
stone, none of which observe a fixed and invariable order 
of superposition. The ancient borders of the lake wherein 
the fresh-water strata were accumulated may generally be 
traced with precision, the granite and other ancient rocks 
rising up boldly from the level country. The actual junc¬ 
tion, however, of the lacustrine beds and the granite is rare¬ 
ly seen, as a small valley usually intervenes between them. 
The fresh-water strata may sometimes be seen to retain their 
horizontality within a very slight distance of the border- 
rocks, while in some places they are inclined, and in few in¬ 
stances vertical. The principal divisions into which the la¬ 
custrine series may be separated are the following:—1st, 
Sandstone, grit, and conglomerate, including red marl and 
red sandstone; 2dly, Green and white foliated marls; 3dly, 
Limestone, or travertin, often oolitic in structure; 4thly, 
Gypseous marls. 
The relations of these different groups can not be learnt 
by the study of any one section ; and the geologist who sets 
out with the expectation of finding a fixed order of succes¬ 
sion may perhaps complain that the different parts of the 
basin give contradictory results. The arenaceous division, 
the marls, and the limestone may all be seen in some places 
to alternate with each other; yet it can by no means be af¬ 
firmed that there is no order of. arrangement. The sands, 
sandstone, and conglomerate constitute in general a littoral 
group; the foliated white and green marl, a contemporane¬ 
ous central deposit more than 700 feet thick, and thinly foli¬ 
ated, a character which often arises from the innumerable 
thin shells or carapace valves shed by the small crustacean 
