Page:Popular Science Monthly Volume 43.djvu/330

From Wikisource
Jump to navigation Jump to search
This page has been proofread, but needs to be validated.
316
THE POPULAR SCIENCE MONTHLY.

only rational course is that of bearing the misery which must be entailed for a time by desistance. The transition from State-beneficence to a healthy condition of self-help and private beneficence, must be like the transition from an opium-eating life to a normal life—painful but remedial.

 

ARE THERE EVIDENCES OF MAN IN THE GLACIAL GRAVELS?
By Major J. W. POWELL.

THE geologist studying in the Rocky Mountains is ever astonished at the rapid degradation of mountain forms. Cliffs, peaks, crags, and rocky scaurs are forever tumbling down. The rocks break asunder above and roll down in great slides on the flanks and about the feet of the mountains. As the slopes are thus diminished, gradually the slides are covered with soil, in part through the decay of the rocks themselves, in part by wind-drifted sands, but perhaps in chief part by the washing of the soils above. In this manner a great mountain is ultimately buried by overplacement. This overplacement gradually washes down, to be distributed on still lower grounds, but it is replaced from above from the newly formed soils. The process goes on until the mountain is degraded into hills and the streams have carried away the greater part of the material of the ancient mountain. Now, in studying these mountains, the geologist is always on his guard to distinguish overplacement from foundation structure. When the mountains are all gone the hills are degraded in the same manner, and the process continues until a grand base-level is established, below which degradation can not take place; then the mountains and hills have all been carried away by rivers to the sea. As mountains and hills are degraded, so valley slopes are brought down. The river, meandering now on this side and now on that, increases the length of its course, as every bend throughout the valley is cut back; but ultimately bend works back against bend, until shorter channels are produced. By cutoff channels the course of the river is diminished; by increasing its meanders the course of the river is lengthened; but in the grand operation the one about compensates for the other. In this manner the river is forever rearranging the flood plain. The banks of the stream, left dry by the vicissitudes of river cutting, tumble down, and a bank goes through a process much like that of the mountain slope; and the geologist is ever on the lookout to distinguish overplacement from the rocks of the foundation structure. There are many conditions where this distinction is plain.