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Page:Popular Science Monthly Volume 24.djvu/256

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THE POPULAR SCIENCE MONTHLY.

root-fibers, and lined with a thin coating of carbonate of lime. The direction of these canals being always from above downward, cleavage in the loess mass, irrespective of size, is invariably vertical, while, from the same cause, water in falling upon a deposit of this material never collects in the form of puddles or lakes on its surface, but sinks at once to the local water-level.

The loess territory of China begins, at its eastern limit, with the foot-hills of the great alluvial plain—roughly speaking, upon the line drawn from Peking to Kaifung in Honan. From this rises a terrace of from ninety to two hundred and fifty feet in height, consisting entirely of loess; and westward of it, in a nearly north and south line, stretches the Tai-hang Shan, or dividing range between the alluvial land and the hill-districts of Shansi. An almost uninterrupted loess-covered country extends west of this line to Lake Koko-nor and head-waters of the Yellow River. On the north the formation can be traced from the vicinity of Kalgan, along the water-shed of the Mongolian steppes, and into the desert beyond the Ala Shan range. Toward the south its limits are less sharply defined; though covering all the country of the Wei basin (in Shensi), none is found in Sz'chuen, due south of this valley, but it appears in parts of Honan and Eastern Shantung. Excepting occasional spurs and isolated spots, loess may be considered as ending everywhere on the north side of the Yangtse Valley, and, to convey a general notion, as covering the parallelogram between longitudes 99° and 115° east, and latitudes 33° and 41° north. The district within China Proper represents a territory half as large again as that of the German Empire, while outside of the provinces there is reason to believe that loess spreads far to the east and north, possibly in varying thicknesses quite across the desert. Baron von Richthofen observed this deposit in Shansi to a height of 7,200 feet above the sea, and supposes that it may occur at higher levels.

One of the most striking as well as important phenomena of this formation is the perpendicular splitting of its mass—already referred to into sudden and multitudinous clefts that cut up the country in every direction, and render observation as well as travel often exceedingly difficult. The cliffs, caused by erosion, vary from cracks measured by inches to canons half a mile wide and hundreds of feet deep; they branch out in every direction, ramifying through the country after the manner of tree-roots in the soil from each root a rootlet, and from these other small fibers until the system of passages develops into a labyrinth of far-reaching and intermingling lanes. Were the loess throughout of the uniform structure seen in single clefts, such a region would indeed be absolutely impassable, the vertical banks becoming precipices of often more than a thousand feet. The fact, however, that loess exhibits in every locality a terrace formation, renders its surface not only habitable, but highly convenient for agricultural purposes; it has given rise, moreover, to the theory advanced by Kingsmill and