2o6 The American Geologist. "^p"'- ^^^^• 
supposed that trees and grass grew on deposits of loess, be- 
cause such deposits furnished favorable conditions. It is now 
maintained that the loess accumulates where trees and grass 
.grow, because it is there readily lodged and protected. 
So strong is this evidence that nearly, if not quite, all of the 
Iowa geologists accept the theory.* But, on the other hand, 
there are so many facts looking in a contrary direction, that 
those familiar with them could not well rest in the simple hy- 
pothesis of the aeolian origin of the deposits. Prominent among 
these facts is (i) the distribution of the loess in about equal 
proportions upon both sides of the Missouri river. At Omaha 
the bluffs of loess on the west side of the river are scarcely, if 
anv, less in dimensions than those of Council Bluffs upon the 
east side. In both cases a depth of one hundred feet is not in- 
frequent. Farther down the river the deposits at St. Joseph, 
Mo., upon the east side, are indeed excessive, but this is read- 
ily accounted for by the direction of the currents, of the river, 
and by the concentration at that point of the sediment brought 
down from Iowa by various streams, whose headwaters were 
near the border of the lowan ice ; the Xishnabotna, the Tarkio, 
and the Nodaway being noteworthy contributors of material to 
the valley above St. Joseph ; while the Platte and the Missouri 
approach each other to within a few miles at St. Joseph. But 
at Leavenworth, upon the western side of the river, and at 
Kansas City, upon the southwestern side, the deposits of loess 
are also on a very extensive scale. 
As the prevailing wind in this region is from the southwest, 
it would be hardly possible for it to pile up such deposits of 
loess upon the west side of the river, and especially upon the 
southwest side, as at Kansas City. 
Secondly, the exclusive dependence upon wind for the dis- 
tribution of the loess finds it difficult to account for the exten- 
sive level-topped terraces which frequently occur. At Omaha 
there is such a terrace in the upper part of the city about 150 
feet above the present river level. At St. Joseph the deposit 
is much eroded by small streams, but the general level of many 
summits, at about 200 feet above the river, is in striking con- 
trast to the surrounding higher land ; while at Leavenworth a 
*J. A. UnDEN, "Report on Mills and Fi-cmont Counties." la. Ocol. Sur., 
vol. xiii. p. 174. in()2; T. K. Savage, "Geology of Tama County." p. 242. 
