Page:The Journal of geology (IA journalofgeology21894univers).pdf/334

In dynamical geology there is one line of inquiry which has received, comparatively speaking, but little attention from American geologists. Our text-books discuss in a thorough manner the work performed by water, and they also tell us much about the work of earthquakes, of volcanoes, and of glaciers. Some of these phenomena appear so striking as always to challenge our attention. Others are so common in their occurrence and so obvious that they suggest themselves to our study and to our reflection everywhere. The work performed by the winds in the atmosphere appears hardly to have received its due share of attention. The transportation of solid materials by the air is one of those subtle operations in nature, which are apt to escape our observation. The process is of an unobstrusive nature, and only in certain localities becomes at all obvious. There are, however, some scientists who have understood and urged the great importance and efficacy of aerial transportation in geological dynamics. Ehrenberg, Von Richthofen and Pumpelly will be remembered first in this connection. Blake, Gilbert, Hayden, N. H. Winchell, Chamberlin, Merrill, and others have described instances of erosion and transportation by the atmosphere. But it will be conceded, I think, that the subject has not received any general and searching attention from geological students in this country. This is the only excuse for presenting at this time a few considerations bearing on the topic. I take the liberty to state in a dogmatic way what appear to me to be some laws governing aerial erosion, transportation and sedimentation in general. It is not claimed that these statements contain much that is new in substance.

As an agent of erosion air is far less efficient than water.