SOME GEOLOGIC ASPECTS OF CONSERVATION 
153 
measures on the ground sixty by forty feet and rises above the 
surface twenty feet. The Iowan drift, in northeast Iowa, is 
especially noted for these monuments of bygone events and has 
more large bowlders than any of the other drift sheets in the 
state. Something should be done to preserve the most notable 
of these glacial bowlders in view of their unique origin and char- 
acter. If nothing is done to prevent it they will ere long be 
sacrificed to the desires of their present owners for convenient 
building material and will be entirely lost to posterity. 
Closely associated with the glacial deposits of the state and 
yet only partly related to them in origin is a remarkable for- 
mation known as the loess. In northeastern Iowa it is derived 
directly from the Iowan drift but along the western margin of 
the state it owes its origin to the great quantities of silt brought 
down and deposited by Missouri and Big Sioux rivers. From 
their flood plains it is picked u;p and carried away by the winds 
to be dropped over the clay hills in an ever-thinning mantle with 
increasing distance from the source. I do not recall that I have 
heard or seen these loess bluffs mentioned in conservation dis- 
cussions, but there is no room for doubt that both botanists and 
geologists will agree in commending them for eareful considera- 
tion. The fact that wind blown deposits with thicknesses of 
fifty to one hundred feet have been shaped into such striking 
topographic forms as are found along these bluffs, and the fur- 
ther fact that they bear what is in reality a desert type of vege- 
tation, and this in the most fertile state in the world, are facts 
which entitle them to recognition in any plans for conservation 
of our beauty spots. The beautiful park at Council Bluffs with 
its winding valleys and steep slopes is sufficient witness to what 
is possible with these loess hills, but there should be preserved 
in an absolutely natural state a tract which would permit of the 
retention both of the original topographic forms and of their 
remarkable vegetal covering. Such areas are available near Mis- 
souri Valley, or near Turin, in Monona county, or in the vicinity 
of Sioux City, and at other localities where the phenomena are 
equally striking. 
In the extreme northwest corner of Iowa, occupying an area of 
not over five acres is a little spot which is unique in its interest. 
This interest arises both because of its rock exposures, which are 
scores of miles distant from any others in Iowa, with the excep- 
tion of a similar one a mile away, and because of the fact that 
