R. Pumpelly—Secular Rock-disintegration. 139 
evidence indeed is all the other way. And yet, while the rocks 
of Southern Asia show extensive residua of disintegration, the 
results of a secular decomposition protected from erosion b 
abundant vegetation, the feldspathic rocks of Northern China 
and of Central Asia are as free from this as are those of north- 
eastern America. 
The only answer to the question, what has become of them? 
is, that they have been blown and sifted and assorted by the 
winds, the heavier fragments remaining to be reduced by weath- 
ering and to form the stony steppes, the sand drifting in bil- 
lowy waves over the country, and forming sand-deserts, while 
the fine dust floating in the air, an impalpable powder is depos- 
ited far and near, and, under the influence and protection of 
the steppe grasses, is transformed into the loess. 
It is not many years since the glacial “till” was recognized 
these deposits seems to me to necessitate a recognition of the 
importance of the great residuary deposits as the source of both 
the others. 
We have here suggestions that bear on many and varied geo- 
logical problems, some of these which now occur to me I ma 
be permitted to mention. 
There are few problems in dynamical geology that have been 
considered more difficult to solve than the origin of rock-basins, 
Wherever my route between the great wall of China and the 
Siberian frontier lay through a region of crystalline rocks, I 
e 
has not lived through at least one great storm on a desert. In such a simoon the 
atmosphere is filled with a driving mass of dust and sand which hides the coun- 
f =F 
ften-cited instances of far-driven volcanic ashes show the ability of the 
i through distances of several hundred 
Wind to carry comparatively coarse dust 
mules, but it does not seem improbable that the finer particles may remain sus- 
pended while the wind makes a complete circuit of the globe. 
and left only a just perceptible film of dust, observable only on the white newly- 
Painted deck of a nit gg A similar fog occurred sim taneously at Shanghae, 
pies both were cotemporaneous with a terrific Awe storm which during two days 
Shrouded the country about Tientsin in deep darkness. 
I am indebted sé to Mr. Clarence King, for the statement that dust fogs 
ur on the coast of California with the prevailing west wind; and this may be 
4s he suggests, the finest residuum of the lcess dust of an Asiatic dust storm. 
