ARCHEAN AND PALEOZOIC GEOGRAPHY 463 
of the extensive mountain growth which was about to 
begin. The beaches and off-shore deposits that had 
been accumulating since the Cambrian, were now in- 
volved in a series of folds, and raised into mountains 
much higher than the present Appalachians. Out of 
these, later denudation has carved the mountain ridges, 
at the same time reducing the elevation. 
Mountain folding has occurred in the west, but here, 
as in the preceding ages, the history of the geological 
development is only obscurely understood. In Texas, 
Kansas, and other parts of the west, the real coal- 
forming period of the Carboniferous was succeeded by 
the Permian division, which in that part of the coun- 
try was tharked by a climate sufficiently dry for the 
development of dead seas. 
The coal period of this section had been one of equable, moist 
climate. It was succeeded by aridity, and the most reasonable ex- 
planation of this is the development of western mountains, which 
rose to a sufficient height to cut off the west wind, and transform 
the region to a condition of dryness, just as the Sierra Nevada 
and Rocky Mountains cause an arid climate in the great western 
region of to-day. During this arid part of the Carboniferous, 
extensive salt lakes existed in various parts of the west; and in 
the bottom of these great inland seas, beds of salt and gypsum 
were deposited. Both in Kansas and Texas, man is now utilizing 
these as a source of salt, by penetrating the earth with borings 
and bringing the salt to the surface. 
