124 Gy Uh, SEWEIRIRM ETE 
and alkaline salts are also driven with the gypsum but on account 
of their solubility they do not remain in the dunes. These dunes 
lie to the south and east of the flats whither they are driven by 
the prevailing winds and not only cover a large part of the 
salinas themselves, but form.a growing fringe to the east and 
south. The dunes are, in the majority of instances, very pure 
gypsum though there is a small commingling of earthy impurities. 
The soil underneath is impregnated with salt and soda and salt 
lakes are scattered over the area covered by the dunes. The 
intervals between the crests of the ridges support a scanty but 
very interesting vegetation. Near the southeastern angle of the 
sands is a very important salt lake which has been known as a 
source of salt for the ranches for many years. The north and 
south extent of the ‘‘white sands”’ is about 35 miles while 
the greatest breadth at the southern margin is about 18 miles. 
The lines connecting the extreme points are irregular, enclosing 
roughly a triangle of about 350 square miles. To this may be 
added nearly as much more of saline land on the west and in 
isolated areas to the south. The whole plain is geologically of 
the same nature, but, inasmuch as it is either higher than the 
basin or is more completely drained (to the south), the saline 
ingredients are not brought to the surface. 
East of the Jarillas Mountains this plain again gives external 
evidence of its subterranean supply of salines while far to the 
north, beyond the covering of lava, there are depressions of the 
same character and of the same geological age and nature. The 
fact that such depressions occur in New Mexico only in connec- 
tion with the red beds leads to a suggestion that may be worthy 
of consideration. It is evident to anyone who has studied the 
geology and geography of the territory that it is, as Major 
Powell said long ago, the best drained region in the world. The 
comparative newness and permeableness of its strata all militate 
against the formation of local basins. There has been no glacia- 
tion to produce local lake reservoirs. Erosion has kept well in 
advance of secular changes of level and barriers of local origin 
do not prove capable of retaining the waters which come in 
