62 
IOWA ACADEMY OF SCIENCE Voi,. XXVIII, 1921 
inches thick. They are tilted to the north and are surrounded 
by the gray loess except where they rise to the surface of this 
stratum and come in contact with the overlying till. These lenses 
were stated by Dr. Charles Keyes in conversation to be largely 
volcanic ash, and this may indeed be true, since ash beds are known 
elsewhere in Iowa and neighboring states. Most conspicuous, per- 
haps, in our own state is the two foot bed exposed at several 
points in the northern part of Harrison county near the village of 
Kittle Sioux along the east bank of Little Sioux river. While the 
presence of this ash bed was known to science previously it was 
only after repeated examinations of its outcrops during the sea- 
son of 1921 that Dr. Geo. F. Kay felt justified in forming the judg- 
ment that the evidence warrants the interpretation that the vol- 
canic ash is contemporaneous with the loess. The evidence of this 
judgment will be presented by him in a forthcoming publication. 
According to this interpretation, then, the relationships of this ash 
bed would be similar to those of the lenses in the Des Moines cut 
— both would be related to the Peorian loess. Samples of the 
Harrison county ash in the office of the Iowa Geological Sur- 
vey show it to be almost white with a finely gritty feel. 
Above the loess is Wisconsin till, which on the average is six 
feet thick. In most places it is weathered through its entire thick- 
ness to a brownish joint clay. It is very characteristic in bearing 
numerous bowlders and cobblestones, many of which are lime- 
stone. 
The sections described above, as will have been seen, are quite 
normal in their main aspects, and in so far may be duplicated in 
many other localities. Some of them present slightly unique phe- 
nomena, such as the ash bed on 5th Street and the intermingling 
of fossiliferous loess and pebble-bearing till in the Court Avenue 
cut. These features as well as their normal characters perhaps 
make them worthy of mention as illuminating the complex record 
of the Pleistocene epoch in the Mississippi valley and the large 
part our state must play in the unfolding of that record. 
They are of value in another way and that is in what they show 
of the physiographic history of this region. We know that an 
immense interval must exist between the deposition of the Coal 
Measures and the advance of the glaciers of Pleistocene time. 
During this interval several successive topographies were incised 
into the face of Iowa, only to be repeatedly wiped off as a school- 
boy wipes his slate, or did when he had one. But of the Pleis- 
