PLEISTOCENE LOAMY DEPOSITS. 167 



increasing in thickness. It is this continual growth of the 

 grasses, keeping pace as it were with the periodical accumula- 

 tion of soil, which, according to Eichthofen, produces that peculiar 

 porous capillary structure which has been described above as 

 characteristic of typical loss. He also insists upon the fact that 

 the organic contents of the Chinese loss pertain exclusively to 

 terrestrial forms — to land-shells and land-animals — the remains 

 of which occur at all depths in the accumulation. 



As the shells met with in the Chinese loss belong exclusively 

 to living species, and the deposit is unquestionably of a recent 

 geological age, this theory of its origin implies an amount of 

 atmospheric disintegration and wind-transport and accumulation 

 which it is hard to conceive could have taken place within the 

 time required. Nor is this difficulty much lessened if we allow 

 with Professor Pumpelly that the materials of the loss had 

 already been prepared for the wind during the lapse of long ages 

 by the action of rain and rivers, frost, snow, and ice ; so that all 

 the wind has done has been merely to redistribute alluvial and 

 other similar materials, and to remove the loose insoluble pro- 

 ducts of a previously long-continued disintegration of the rocks. 

 It may be that we have hitherto underestimated the action of 

 winds as geological agents in dry continental areas like those of 

 Central Asia, and that aerial currents have played a much more 

 important rSle in the past than has been generally supposed. 

 " No one," Mr. Pumpelly remarks, " can realise the capacity of 

 wind as a transporter of fine material who has not lived through 

 at least one great storm on a desert. In such a simoom the 

 atmosphere is filled with a driving mass of dust and sand, which 

 hides the country under a mantle of impenetrable darkness, and 

 penetrates every fabric ; it often destroys life by suffocation, and 

 leaves in places a deposit several feet deep." x But such rapid 

 accumulation occurs, I presume, only in the desiccated desert 

 itself or its immediate neighbourhood. Deserts of shifting sand 

 increase their bounds by a gradual encroachment, the dunes of 

 the peripheral regions continually advancing in the direction of 



1 American Journal of Science and Art, vol. xvii. (1879), p. 139. 



