712 The Chinese Loess Puzzle. [ December, 
would appear that no other theory than this can be adopted for 
their explanation. A marine origin is rendered impossible by 
the absence of marine fossils, the constant presence of land shells 
and bones of land animals, as also by the absence of stratification 
and the very great differences of level at which the formation 
rests. The same arguments apply to the theory of a lacustrine 
origin, except that the one last mentioned would not present in- 
superable difficulties, or at least not any greater ones than those 
which the adoption of Richthofen’s views implies. Either theory 
seems to need for its support changes of climate and a certain 
amount of alteration in the configuration of the surface. If the 
loess were deposited in closed basins, these are now opened to the 
sea and drained by the Hwang-Ho. The areas once separated 
from each other are at present connected; the deposits they in- 
closed are now being swept away to the sea. It is impossible to 
account for this changed condition of things without admitting 
a considerable increase in the amount of precipitation over the 
region in question, and it is not easy to see how a complete 
` drainage system could have been established without the forma- 
tion of a certain number of lakes, nor why these should all have 
disappeared so completely. Acéording to the lacustrine theory, 
on the other hand, the precipitation is now less than it formerly 
was ; the mighty lakes have shrunk and disappeared, the Hwang- 
Ho is but the remnant of what was once a much larger stream. 
What change of level in the area thus drained would be required 
to fit this theory it seems difficult to make out. The appearance, 
in a future volume of Richthofen’s great work, of the details of 
the cartography and geology of the region in question will, no 
doubt, be of much assistance in enabling one to form a clearer 
opinion of these matters. The interesting chapter in the volume 
already published, entitled Formation and Remodeling (Bildung 
und Umbildung) of the Salt Steppes of Central Asia, in which 
subjects closely connected with the question of the mode of for- 
mation of the loess are discussed at very considerable length, 
cannot at present be entered upon, for want of space. Its con- 
sideration may be taken up at a future time, when it will be 
found that it has important bearings on certain points closely m 
lated to our own surface geology, and which have not yet received 
anything like the attention which they deserve at the hands of | 
our geological observers. It is sufficient, for the present, to have 
given the readers of the NATURALIST an idea of one among the 
many interesting topics treated in Richthofen’s work. It 
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