TRANSPOETATION BY EUNNIisG WATER. 13 



year there is consideraole blowing- of tlie clay and the finer grains of the 

 till or gravel, especially on dry hillsides. It is this blown soil which so 

 often covers the snow in winter. It is well known that in exposed situa- 

 tions fall plowing results in a considerable loss of soil. Often in hillside 

 pastures little cliffs of wind erosion can be seen, worn away partly by the 

 direct impact of the wind and partly by the sand and small gravelstones 

 blown against their sides. In this way considerable areas have been 

 denuded of their surface layers. To this process I have elsewhere given 

 the designation " till -burro wing." It is by far most active along the borders 

 of di-ifting sand dunes, partly because the protecting vegetation has been 

 killed by the sand, and partly because in such situations the surface is 

 drier than usual. Thus en a hilltop about IJ miles northwest of Wayne 

 Village, chffs in the till were 3 feet high and the till was eroded to the 

 solid rock. The finer parts were driven away and the rock was strewn 

 with the larger stones of the till. The gravel thus left is to be distinguished 

 from the other foiTQS of gravel. 



The process of till-buiTowing is often aided by sheep, which have a 

 habit of digging into hillsides in order to lie in the shade of the small cliff's 

 thus formed. 



TRANSPORTATION BY RUNNING WATER. 



This is the most common and familiar of all the natm-al processes of 

 di-ift transportation. The power of running water to transport solid frag- 

 ments depends on several elements: (1) According to Hopkins, other tilings 

 being equal, the power to transport increases as the sixth power of the 

 velocity. (2) Since in general the force of gravity is to be overcome, it is 

 ob^^ous that the specific gradty of the di-ift matter is to be taken into the 

 account. (3) The shape of the fragment to be transported must also have 

 an influence on the result, since this determines the relative amount of sur- 

 face presented to the force of the cmrent and often the friction to be over- 

 come ; thus spheres are more easily transported than slabs having the same 

 weight. (4) The volume of the current must also be considered. Rocks of 

 the ordinary kinds have a specific gravity of 2.4 to 3. When submerged 

 they lose one-third or more of their weight, and they will be more easily 

 transported when there is volume of water sufficient to wholly submerge 



