PL^EISTOCENE EXPOSURES IN DES MOINES 
61 
was hard with a starchy fracture. Both the red and yellow phases 
were non-calcareous. Possibly this till was derived in considerable 
part from the underlying shale. The upper red portion evidently 
is nearly at the gumbotil stage of weathering. This phase showed 
a thickness of seven feet. 
There seems to be no sufficient reason or necessity for consider- 
ing the older till in this cut as being other than Kansan. There is 
nothing in its stratigraphic position or its physical characters which 
is in any sense determinative. Experience has abundantly proved 
that there are no physical criteria which will differentiate between 
Kansan and Nebraskan tills. Neither color nor texture nor pebble 
content offer conclusive testimony. Till has been found which is 
known from its relations to be Nebraskan and yet it is as light a 
gray as socalled ''typical Kansan till,” and has similar structure 
and pebble content. The converse is equally true—instances could 
be cited of till positively known to be Kansan which is dark gray 
to black and not more pebble-bearing than Nebraskan till. The 
abolition of the very comfortable criterion of physical character 
throws the geologist back into the realm of uncertainty unless he 
can substantiate his claim by stratigraphic methods, such as the 
presence of gumbotils or soil bands. In the present case we can 
only say that there is nothing to indicate that this till is older than 
the Kansan, since, be its color blue, yellow, or brown, that is mere- 
ly a matter of oxidation and this may transpire with equal readi- 
ness in one till or in another. 
In the vicinity of Chestnut Street the upper surface of the Kan- 
san is practically level but between Center and Crocker streets is a 
small knoll of this till which rises about fifteen feet above the level 
of the till at Chestnut. About five feet of brown, pebbly till with 
starchy fracture is exposed at this point in the cut. Some fresh 
red granite bowlders are present at the surface of the till. 
Over the Kansan till and exposed along almost the entire extent 
of the cut, about six blocks, is the loess, which in places has a 
thickness of fifteen to eighteen feet. It is chiefly of the yellow 
phase, although in places there is three or four feet of gray at the 
top and this is locally marked off at the base by a ferruginous band 
which seems to mark a former water surface. In places fossils 
are common in the yellow loess while red "pipe-stems” abound in 
the gray variety. Both phases are calcareous. 
In the vicinity of Crocker Street there are in the upper portion 
of the loess several small sand lenses about four feet long and six 
