1877. ] The Chinese Loess Puzzle. 711 
no longer there ; but the constant occurrence of innumerable del- 
icate, elongated cavities, occupying a nearly vertical position, 
ramifying and inosculating at very acute angles, just as do the 
rootlets of plants, shows their former presence. It is to this 
peculiarity that the tendency to vertical cleavage, which is so 
conspicuously manifested in the loess, is largely due. 
There is a greater difficulty still, if possible, in the way of the 
adoption of the lacustrine origin of these deposits. As Richt- 
hofen declares with the utmost confidence, based on a thorough 
examination of the region, the loess everywhere exhibits itself as 
a deposit which was not laid down until after the surface of the 
country where it occurs had assumed its present configuration. 
The orographic conditions are not such as, by any possibility, 
could allow of the formation of a connected series of lake-like 
expansions of the Hwang-Ho, as is demanded by Professor Pum- 
pelly’s theory. 
Richthofen, therefore, unhesitatingly declares himself in favor 
of a subaerial origin of the loess ; and he endeavors to account for 
the accumulation of this enormous mass of material in the follow- 
ing manner. In the first place, and as a necessity of the pro- 
posed theory, the district of the loess was once destitute of out- 
ward drainage, consisting, in fact, of a number of closed basins, 
such as are still found occurring in the adjacent region to the 
west in Central Asia. These closed basins were prairies, and 
_ the loess is “ the collective residue of uncountable generations of 
herbaceous plants.” It is the inorganic residuum which has ac- 
cumulated during an immense lapse of time as the result of the 
decay of a vigorous prairie growth, ever renewing itself on the 
surface of the slowly accumulating deposit. But how is the in- - 
crease of the deposit provided for by the theory ? Unless there 
be some source supplying material from without, there can evi- 
dently be no gain in thickness, however many generations of | 
plants succeed each other. The necessary addition of mineral 
matter Richthofen considers to have been brought into these ba- 
sins by two agencies, the rain and the wind, and the latter es- 
— pecially plays an important part in this theory. Each basin be- 
ing surrounded by a rim of rocks, constantly undergoing decom- 
= position, the particles thus set free were either swept down the 
- Mountain sides towards the central area by rain, or blown thither 
by air currents, and once entangled among the vegetation could 
not be carried farther. : 
The facts being assumed to be as Richthofen states them, it 
