GLACIAL DEPOSITS OF THE CONTINENTAL TYPE 299 
Relationships of occurrence.—Most of the localities where loess 
soil has thus far been observed in Alaska are upon the edges of 
bluffs or within a mile or two of the rivers. Here vast quantities 
of gravel, sand, and fine silt are being transported by the present 
glacial streams, which have rather steep grades and flow 5 to 7 
miles per hour. The grade of the main Copper River, for example, 
averages 7 to 12 feet to the mile, in contrast with the Mississippi 
and Ohio whose grades average less than half a foot to the mile. 
The mean annual rainfall in the Copper River basin js about 
—- ‘ 4 a 
CI ae 
Fic. 4.—Mature forest growing upon wind-blown deposit, Copper River basin, 
Alaska. 
363 inches, only 3 or 4 inches of which come during the summer 
months when the snow is off the ground. The deposits left by the 
rivers at low water are, therefore, normally dry and easily blown 
about by the wind. Severe sand and dust storms are prevalent, 
indicating the origin of these loessian accumulations in Alaska as 
wind-blown deposits. We ourselves have witnessed these severe 
dust storms in 1910 and tori and they have been reported by 
many others from Copper River basin and adjacent regions.’ 
Rohn states, for example, that on one occasion in 1899 the material 
whipped up from the outwash plain “‘ was so thick that it was impos- 
tOscar Rohn in W. R. Abercrombie’s Copper River Exploring Expedition, 1599, 
Washington, Government Printing Office, tg00, p. 127. 
