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THE POPULAR SCIENCE MONTHLY 



sumes a blue color wherever the perchloride 

 is unaltered, all the rest of the surface re- 

 maining white. The image is then freely 

 washed in water, and passed through a bath 

 of chlorhydic acid (8 to 10 parts to 100 of 

 water), which removes the protoxide of iron 

 salt ; it is then washed again in water, and 

 finally dried. The drawing then appears in 

 blue lines on the pure white ground of the 

 paper. 



The Chinese Loess or Loam Deposits. 



The origin of the " loess " deposits of China 

 has long been a perplexing problem for ge- 

 ologists. This deposit is spread almost con- 

 tinuously over an area as large as the Ger- 

 man Empire, besides existing in detached 

 areas of nearly half that extent. Usually, 

 the loess is several hundred feet in thick- 

 ness, and in some places as much as 1,500 

 or even 2,000 feet. It is an earthy sub- 

 stance, of a brownish-yellow color, friable, 

 chiefly consisting of argillaceous materials, 

 with a small proportion of carbonate of 

 lime ; it has also mixed with it more or less 

 of fine sand, the grains of which are very 

 angular. The Baron von Richthofen, in his 

 work on " China," the first volume of which 

 has appeared, offers the most satisfactory 

 theory yet presented of the origin of this 

 loess. A very clear statement, both of the 

 problem itself and of Von Richthofen's solu- 

 tion of it, is given by Prof. J. D. Whitney, 

 in the American Naturalist, who states that 

 the first geologist to notice and describe 

 these remarkable deposits was Prof. Pum- 

 pelly. According to him, the loess of China 

 is a lacustrine formation, each of the basins 

 in which it occurs having been once the bed 

 of a lake. But the absence of stratification 

 and of fresh-water shells, and the presence 

 of the bones of land - animals, appear to 

 be utterly incompatible with this theory. 

 Besides, the loess indicates by its structure 

 the growth on its surface of an abundant 

 vegetation. But a greater difficulty still 

 stands in the way of the theory of a lacus- 

 trine origin namely, the fact that every- 

 where the loess plainly shows itself to be a 

 deposit which was not laid down till after 

 the surface of the country had assumed its 

 present configuration. Hence Richthofen 

 unhesitatingly declares himself in favor of 

 a subaerial origin of the loess. Wind and 



rain are, according to him, the agencies 

 which produced these deposits. In the first 

 place, he assumes the district of the loess 

 to have been once destitute of outward 

 drainage, and to have, in fact, consisted of 

 a number of closed basins, such as are still 

 found in the adjacent region, to the west, in 

 Central Asia. These closed basins were 

 prairies, and the loess is the collective resi- 

 due of innumerable generations of herbace- 

 ous plants. It is the inorganic residuum 

 which has accumulated during an immense 

 lapse of time, as the result of the decay of 

 a vigorous prairie-growth, ever renewing it- 

 self on the surface of the slowly-accumu- 

 lating deposit. But how is the increase of 

 the deposit provided for by the theory ? 

 Unless there be some source supplying ma- 

 terial from without, there can evidently be 

 no gain in thickness, however many gener- 

 ations of plants succeed each other. The 

 necessary addition of mineral matters Richt- 

 hofen considers to have been brought into 

 these basins by two agencies, the rain and 

 the wind, and the latter especially plays an 

 important part in his theory. Each basin 

 being surrounded by a rim of rocks, con- 

 stantly undergoing decomposition, the par- 

 ticles thus set free were either swept down 

 the mountain-sides toward the central area 

 by rain, or blown thither by air-currents, 

 and, once entangled among the vegetation, 

 could not be caried farther. 



The Pennsylvania Oil-Regions. The oil- 

 regions of Pennsylvania are, in an article by 

 M. C. A. Ashburner, in the Journal of the 

 Franklin Institute, divided into three dis. 

 tricts, the southwestern, the western, and 

 the northern, the southwestern lying south 

 of the Ohio and west of the Monongahela, 

 the western occupying the water-basin of 

 the Alleghany, between Pittsburg on the 

 south and the Philadelphia & Erie Railroad 

 on the north, and the northern district ex- 

 tending north from the line of the same 

 railroad. In the first of these districts the 

 petroleum comes from the highest rocks, 

 and in the third from the lowest, while in 

 the second it comes from the rocks inter- 

 mediate between the two. The " oil-sand 

 group " of the southwestern district is com- 

 posed of three sandstone members, sepa- 

 rated by intervals containing coal-seams, 



