On the Physical Geography of the Alps. 377 
formation of the earth; of the influence of glaciers on the de- 
struction of rocky materials, the formation of sand, the transport 
of shingle, land- and mountain-slips, and the movement of great 
masses of débris 
in the regular course of many rivers in transverse valleys is fre- 
quently between 7 and 11 Paris feet per second. Their velocity, - 
however, is at other places so considerable, that they have always 
force sufficient to move small shingle :—5. ‘The quantity of mat- 
ter held in suspension in glacier-brooks and all Alpine streams 1s 
usually very great, and exceedingly increases their eroding power: 
—6. By erosive action the bed of a river may be very deeply ex- 
cavated in the hard rock: such channels reach their utmost de-, 
Velopment in the more inclined ravines; they remain, however, 
washed down and deposited about at different places :—8. ‘T 
formation of earthy detrital. matter [Erdkrume] by mechanical 
disintegration and chemical decomposition of rocks, proceeds 
