Glacial Deposits in Driftless Area. — Sardeson. 395 
loam is, on the contrary, quite uniform, being about four feet 
or less. Tlie sand forms local patches, while the loess loam is 
continuous with that of distant regions. Consequently the 
source of the sjuid may well be believed to be of local origin 
as explained, the loess, on the contrary, partly local but main- 
ly of foreign origin. The loess could not have been derived 
from the residuary clay of the limestones of the area since 
that clay is still uniforjnlj' covered under the loess; nor from 
a part of that clay unless the same had been uniformly moved 
off and back again, which is difficult to imagine, for so gieat 
a mass. If one consider the loess loam as a residuary clay 
from the Paleozoic rocks he has these objections to answer: 
How could two kinds of residuary clay form, one above the 
other, the lower one with residuary quartz or chert, the upper 
without them: the lower as a ruleon limestone and clay onl}'. 
the upper one on sandstone also; the lower one extending un- 
der the true loess when it is present, the upper one extending 
over the same? The origin of the loess loam was most prob- 
ably from loess, the loess from remote regions chiefly. 
There is found in Minnesota and Iowa evidences of wind 
action on large scale. Especiall}' in Isanti, Anoka and 
Chisago counties of Minnesota, are sands in structure like 
the wind driven sands of the Peccatonica valley. Warren 
Upham has described and interpreted some of them : 
Dunes of sand, gathered from the modified drift by the wind, and 
heaped up in mounds and ridges 10 to 20 feet high, occur in the south 
part of sections 34, 35 and 3(j, Grow, Anoka county. They are blown 
into frequently shifting forms, like drifts of snow, and are too unstable 
to give a foothold to vegetation. It seems most probable that they 
were gathered from the coarser sand and gravel of the surrounding area 
soon after the deposition of these beds, before they became covered, 
and protected from wind erosion, by grass, bushes and trees.'"* 
Colonel Folwell, flrst president of the University of Minne- 
sota has described to me the same kind of an area which for- 
merly existed on and near the present site of the University 
campus. This area was gradually reclaimed mainly through 
the sand-bur, (Cenchrus tribuloides Linne) he informs me. 
Evidence of this area still exists in a deposit of loose sand, 
{see fig. 17, p. 297, op. cit.) covering a long distance. Areas 
*Final Rep. Minn. Geol. Nat. Hist. Survey, vol. ii, p. 418. 
