Review and Comment. 
853 
the Alps are the most thorough, comprehensive, and complete of 
all that have come under my notice. His results are embodied 
in his “Handbuch der G-letscherkunde, ” Stuttgart, 1885. 
It is often stated by writers on the subject of glacial erosion, 
that the amount of sediment carried down by glacial brooks 
and rivers is much greater than that carried down valleys of 
equal area in which there are no glaciers; the obvious inference 
being that ice is much the more effective form of water so far 
as erosion is concerned. 
That such statements are very misleading will be apparent on 
a little reflection. In the first place the measurements on 
which the estimates usually quoted, are based, were invariably 
made during the time when the rate of melting of the ice is at 
its highest. 
Secondly, no deduction is made for material brought into the 
glacial stream by other means than the action of ice; a large 
factor or rather several factors of error thus find their way into 
the problem as commonly presented for solution, and the answer 
can but be erroneous. 
Heim points out these factors distinctly. 29 
An oft-quoted example is that of the stream flowing from the 
Unter Aar glacier. 
In 1841-5 Dolfuss determined the weight of sediment in the 
stream to be 1-7,040 th of the weight of the water. But Heim states 
that these measurements were made in July and August, and that 
the average amount for the year cannot at most be more than 
1-20,000th of the weight of the water. This is a reduction of 
nearly two-thirds from the widely published figures, yet it by no 
means tells the whole story. There are still other corrections to 
be made. It will be noticed first that the precipitation is fully 
as great on this valley as upon an equal unglaciated valley. The 
wash of this rain water from the valley sides and from the 
surface of the moraine covered glacier makes a very large ad¬ 
dition to the sediment of the glacial stream. Again the 
Schmelzicasser itself, armed with the fine sand it carries is a 
powerful erosive agent, and the results of its activities are 
added to the total which goes out from the front of the glacier 
29 op. cit. p. 363. 
