I. 0. Russeli—Subaérial Deposits of North America. 349 
the yellow earth is always dry and powdery. These lakes are 
frequently called “sinks,” as the “sink of the Carson River” for 
example; but a more complete misnomer could scarcely be cited, as 
the water escapes from them solely by evaporation. 
There is one remarkable peculiarity in which the loess region of 
China differs from the Arid Region, that is, it has been deeply 
dissected by stream erosion, so that the vast thickness of its super- 
ficial deposits is fully exposed. In this country the valleys of the 
Arid Region are still being filled, and dissection has not com- 
menced. In China a recent climatic change, perhaps very moderate 
in its character, seems to have occurred, which has allowed of 
the formation of streams in a previously drainless region, and the 
streams have sunk their channels in the loess in the wonderful 
manner described by travellers. 
The similarity between the loess of China and the adobe of 
America is such as to warrant the conclusion that they were 
deposited under essentially the same conditions. That they are 
both mainly subaérial deposits, it seems to me, must be acknow- 
ledged by every one who is familiar with the geological processes 
now active in arid regions. 
Richthofen! refers the origin of the loess of China to three 
processes: “The first is rain water, which flows down from the 
upper to the lower parts, and washes away the solids which have 
become loosened by the decomposition of the rocks of neighbouring 
mountains. The second is the wind, whose extraordinary aid in 
accumulating dust-like divided solid material, one has frequent 
opportunity to notice in the regions occupied by the loess. The 
third agent lies in the mineral ingredients, which the roots of . 
grasses, by the diffusion of mineral fluids drawn up from below, 
assimilate, and on their decay leave behind. All these finely 
divided ingredients are held fast by the vegetable covering, and 
thence afterwards carried away only in small quantities by the 
wind.” 
The second and third of these processes are held by Richthofen 
to be most important; and of these two by far the greater promin- 
ence is given to the second, that is, to the action of the wind in 
transporting dust. My own studies in the arid portions of this 
country failed to sustain this explanation, but lead me to refer the 
accumulation of both the coarse and the fine deposits now accumu- 
lating in the drainless valleys of that region to the first hypothesis 
mentioned above; that is, to the transportation and deposition of 
fine material by ephemeral streams. 
That eolian transportation is an element in the process by which 
inclosed valleys are filled with fine debris must be acknowledged ; 
but that it is the principal, or even an important element, does not 
appear to be warranted by a study of the processes by which such 
deposits are now being formed. 
Richthofen has shown so clearly that the loess of China was not 
accumulated in freshwater lakes or in the ocean, that the hypotheses 
1 China, vol. i. p. 78. 
