284 PHYSIOGRAPHY OF CENTRAL-ASIAN DESERTS AND OASES. 
exposing red layers of laminated sandy clay, and doubtless range across the direc- 
tion of prevalent wind, as there is a constancy of leeward overhanging sides. 
Everywhere they are associated with heaps of sand derived from the silt, of which 
all finer material has been drifted away, doubtless to settle as loess in grassy 
mountain valleys. Anyhow, wherever the finer material is now, it has been 
totally removed by the wind that excavated the trenches and left their sand 
constituent behind. Another interesting feature is the frequency of large masses 
of sand piled on top of these ridges, to occupy spaces of calm in the eddies of 
windwork. 
Proceeding still mountainwards, we soon find these trenches of deflation 
floored by hard gravel-beds, and in the course of a few miles the silt deposit thins 
out and dwindles into spits and iso- 
lated areason the gravel-plain, giving 
it a mottled aspect as seen from a Me 
distance—mottled only inshadeand 934 
texture, as both are red. ‘This is e 
the transition from silt to gravel, 
for in a short distance it is all one 75 
vast expanse of gravel or cobbles 69 
varying up to,4 or 5 inches in size. 647 
grass 
x 
Here, therefore, is record of two 
significant changes of conditions suc- 
ceeding each other—first; a moun- 
tainward recession of alluviation 
bringing its zone of fine deposits over 
its more ancient zone of coarse de- ote 
posits; second, a dissection of both 20st ick 
preceding zones by the channels now 15 Ss gy ‘ne cross -oeaee 
occupied, moving alluviation again 
to a zone farther out than before the treba ra ete 
first change. It may be that the page aL 
first resulted from a decrease of Fig. 462.—Vertical Section of Interlapping Loess and Alluvium in 
precipitation corresponding to that eee ata Canal Comin an 
extreme reaction which followed the 
glacial period, as evidenced by moraine underlying the glaciers of Pamir. That 
the second resulted from an increase of grade caused by an uptilting of the margins 
of Tarim will be shown as we proceed. 
Now we are perhaps 25 miles from the great sand, and our abandoned pied- 
mont develops into a bad-land topography, an inclined table-land dissected into 
a desert of red mountains rising ever higher above us as we ride slowly up the 
bottom of a canyon. At first the canyon walls are built entirely of piedmont 
conglomerates with here and there a layer 1 to 3 feet thick of silt, and all in slope 
conforming to that of the plain above. Then towards the bottom of the wall 
appears a surface beveling the tilted strata of a still more ancient piedmont series, 
Heater y Mate, le! 


