Report of a reconnaissance from Carroll, Montana Territory, on the upper Missouri, to the Yellowstone National Park, and return, made in the summer of 1875 . oods, the waters rise many feet, overspreading the lower alluvial ground,and iu subsiding and evaporating they deposit their load of sand and clay, sometimes covering a well-grown and fertile plain with a bed of alluvium a foot and more in thickness. This sometimes takesplace for a number of successive years at the same points, as is shown by the fact that the rootsof trees which must have been close to the surface of the ground when they
Report of a reconnaissance from Carroll, Montana Territory, on the upper Missouri, to the Yellowstone National Park, and return, made in the summer of 1875 . oods, the waters rise many feet, overspreading the lower alluvial ground,and iu subsiding and evaporating they deposit their load of sand and clay, sometimes covering a well-grown and fertile plain with a bed of alluvium a foot and more in thickness. This sometimes takesplace for a number of successive years at the same points, as is shown by the fact that the rootsof trees which must have been close to the surface of the ground when they commenced to growwere often seen buried beneath from four to six feet of alluvium. We could of course only observetliis on the very edge of the bank, where the water had removed a part of the old alluvium, expos-ing to view the roots, and that part of the trunk whichhad been buried. Some of these trees were quite small,not more than 3 or 4 inches in diameter, and most of themwere still living; thus indicating how rapidly such depos-its as those referred to are made. The trees were mostly @fe- cotton woods and elms, species of rapid growth. That these. deposits are made very rapidly is also shown by the thicklayers to be noticed iu any section of a bank so deposited ^sometimes a foot or more, perfectly homogeneous. It isinteresting to note the great variation in the height of theperpendicular alluvial banks. From point to point, in somecases, it is only three or four feet; in others twenty-five feetor more. This depends obviously on the strength of the current, and the extent to which the wateris backed up. It bears upon the general subject of river-terraces. Not infrequently we observed asecond terrace above, or rather a long line of high cut bluffs separated from the stream by anotheralluvial plain (see figure 3). This is all of recent origin, and merely means that the river stoppedwashing away the bluffs here, and commenced to fill up at its foot. The energy of the stream is
Size: 1835px × 1361px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., booksubje, booksubjectdiscoveriesingeography, booksubjectzoology
