402 
MINERALOGICAL GEOLOGY 
Meyerhoffer, Hindrichsen, and Weigat, in which there is a com¬ 
mon succession of salts thrown down by the progressive evapora¬ 
tion of saline waters. 
Colemanite is doubtless a strictly desert product and is perhaps 
being formed to a limited extent today in such old playa muds 
which are covered with boraciferous waters of Ash Spring in the 
Amargosa Valley, in Nevada, east of Death Valley. These bor- 
ate-ladened waters, soon after gushing forth from the great spring, 
spread out far and wide over the level playa. The wind-blown 
dusts carrying much lime constantly settle in the thin sheet of 
water, or on the mud flat. It may be that the lime borate forms 
when' such spring waters are most abundant, while at other times 
only fine sands and volcanic ash accumulate. 
Keyks. 
Interior Seas of the Arid Region. Ever since the time when 
Whitney, standing on the crest of the Sierra Nevada, gazed out 
over the desert level of the Great Basin which spread out before 
him eastward to the very verge of the world, and observed thdt 
“No doubt at that [former] time the now arid valleys [plains- 
level] of Nevada were beautiful inland seas, which filled the 
spaces between the lofty parallel ridges by which that State is 
traversed,^’ and that “perhaps the slopes of these ridges were then 
clothed with dense forests, offering a wonderful contrast to the 
present barrenness of the ranges, and the monotony and desola¬ 
tion of, the alkaline plains at their base,” many, if not all, of the 
desert deposits have been looked upon as old lake beds. 
In Whitney’s day there was known no such thing as a desert 
geology. It was not even suspected that the intermontane valleys 
were only potential lake basins, that none of these countless basins 
were water wrought, and that few of them had ever been occupied 
by bodies of water, or that the entire landscape was one of erosion, 
the prodigious result of normal deflation in a tract from which 
miles of rock strata had been dislodged and exported on the 
wings of the winds. 
The great lake theory long prevailed. It at length was made 
to cover the continent. The vast fresh-water Tertiaries formed a 
theme that fired the imaginations of many an earth student for 
many a day. Even within the last decade these characteristic clays 
