Prof. Baron F. Richthofen — On the Origin of the Loess. 297 



an horizontal position, extend from the hill-sides for some distance 

 into the accumulation of the Loess itself, separating it in the 

 neighbourhood of the encasing slopes into laj^ers of varying thick- 

 ness, while towards the central portion of each large basin this 

 separation ceases almost completely, and the soil is very homo- 

 geneous from top to bottom, even in those instances where the 

 vertical thickness is 1500 feet and more. 



It is perfectly evident that no theory starting from the hypo- 

 thesis of the deposition of Loess by water can explain all or any 

 single one of these properties. Neither the sea nor lakes nor rivers 

 could deposit it in altitudes of 8000 feet on hill-sides. Origin from 

 water is perfectly unable to explain the lack of stratification, the 

 profuse existence of capillary tubes, the vertical cleavage, the pro- 

 miscuous occurrence of grains of quartz, the angular shape of these, 

 the confused position of the laminge of mica, the imbedding of land 

 shells, and of bones of terrestrial mammals. 



There is but one great class of agencies which can be called in 

 aid for explaining the covering of hundreds of thousands of square 

 miles, in little interrupted continuity, and almost irrespective of 

 altitude, with a perfectly homogeneous soil. It is those which are 

 founded in the energy of the motions of the atmospheric ocean 

 which bathes alike plains and hill-tops. Too little weight has been 

 granted hitherto b}' geologists to these agencies, and yet there is no 

 other which has contributed in a greater measure to determine and 

 to modify the character of the surface of any portion of the ground 

 after its emergence from the sea, and to predestinate wide regions 

 for the existence of certain kinds of plants and animals, and for the 

 modes of nomadic or agricultural life of mankind. 



Wherever dust is carried away by wind from a dry place, and 

 deposited on a spot which is covered by vegetation, it finds a resting- 

 place, and may be washed ofi" and carried fai'ther away by the next 

 rain, if the ground is sloping, or it may be joined to the soil if the 

 ground is flat or slightly inclined. If these depositions are repeated, 

 the soil will gradually grow. At the same depth, therefore, to 

 which the deepest rootlets of the grass of to-day are descending, the 

 soil may have had its surface centuries ago. Eemains of the past, such 

 as buildings and entire cities, may in this way have been entombed 

 by dust, provided that plants were growing on its deposits, and could 

 secure a I'esting-place to all fui-ther supplies of atmospheric sediment. 



In regions where the rains are equally distributed through the year, 

 little dust is formed, and the rate of growth of the soil covered with 

 vegetation will be exceedingly small. But where a dry season 

 alternates with a rainy season, the amount of dust which is put 

 in motion and distributed through atmospheric agency can reach 

 enormous proportions, as is witnessed by the dust storms which in 

 Central Asia and Northern China eclipse the sun for days in succes- 

 sion. A fine yellow sediment of measurable thickness is deposited 

 after every storm over large extents of country. Where this dust 

 tails on barren ground, it is carried away by the next wind ; but where 

 it falls on vegetation, its migration is stopped. 



