230 TJie American Geologist. April, \m^ 
denuded during secondary time, as is shown by the compara- 
tively even overlaps of Jurassic and Cretaceous strata on the 
flanks of the central plateau and elsewhere; but of these buried 
portions no more need be said at present. Continued denuda- 
tion at last reduced the region of the central area itself to a 
surface of moderate relief, and it was upon a surface thu5 
prepared that several brackish Tertiary lakes, communicating 
with the sea on the north and south, laid down their sediments. 
Since then, the region as a whole has been much uplifted, it.^ 
southern and eastern parts have been irregularly dislocated, 
volcanic action has diversified parts of the surface, and denuda- 
tion has effected important changes in the complex uplifted 
mass: but the northwestern part is free from dislocation and. 
from volcanic action, and there the uplifted surface of denuda- 
tion is well displayed in an even plateau ( abstracted chiefly 
from Deperet, Ann. de Geogr., i, 1892, 369-378). If stripped of 
its volcanic cones and flows and 'unfaulted', the plateau would 
have the form of a vast inclined plane, highest in the south- 
east, and descending very slowly to the northwest (Boule, in 
Joanne's Dictionnaire geogr. et admin, de la France, iv, 1895, 
2538). The northwestern part of the plateau, unaffected by 
volcanic action, and not covered by the lacustrine formations 
that elsewhere rest upon it, exhibits a surface of crystalline 
rocks interrupted only by closely folded troughs of coal meas- 
ures, whose outcrops are sharply cut across at plateau hight, 
as if the whole structure had been rubbed down by a great 
levelling machine. The perfect regularity of the uplands be- 
tween Montluqon and Creuse is an excellent representation 
of the form that the whole extent of the plateau region must 
have had about the beginning of Tertiary time, before it was 
uplifted and dislocated. Long continued erosion had then re- 
duced the region to a plain close to sea level, thus destroying a 
great mountain chain and leaving in its place a lowland com- 
posed chiefly of long belts of granitic rocks (Velain, "iVuver- 
gne et Limousin, geographic physique," in " L' Itineraire 
Miriam," Paris, 1897, 10). 
These extracts make it clear that French observers regard 
the stratigraphic evidence of the Tertiary lake deposits as con- 
firming the conclusion reached from the study of form alone; 
both lines of evidence show that the uplifted, dislocated, and 
