50 
IOWA ACADEMY OF SCIENCE Voi.. XXVIII, 1921 
in 1883, similar volcanic glass-dust drifted quite around the world, 
and produced the gorgeous “red sunsets” for many a month after- 
wards. Because of its abundance and of its thickness at Des 
Moines, it is not probable that the site of its origin is so far away 
as the other side of the earth. Most likely the material came from 
some of the later eruptions in the Rocky Mountains or the Pacific 
Coast ranges. 
That the eruption which furnished the glass-dust for the Iowa 
deposit was a notable one, wherever it was, is clearly indicated by 
the depth and volume of the accumulation. In order to attain a 
thickness of six inches or a foot the dust-cloud from the volcanic 
vent must have been driven by a strong and prevailing wind. 
No doubt a like thickness of ash spread over a very large ex- 
panse of country, probably over hundreds, and perhaps even thou- 
sands, of square miles. Except in especially favored localities this 
dust mingled with the soil and the record of its existence was lost. 
The deposit under consideration manifestly owes its preservation 
to the circumstances that the dust settled in a small pool of water 
where it remained undisturbed from further wind action and was 
fully protected from the erosive influence of the rains. 
This notable volcanic ash bed is brought to sky in the course of 
recent extensive grade-cuttings on Fifth Avenue, between Grand 
Avenue and School streets, in the city of Des Moines. With it is 
also exposed one of the finest sections of Glacial deposits ever dis- 
closed within the limits of our state. The longitudinal exposure 
is over half a mile, and the vertical cut is 50 feet as a maximum. 
It is essentially a north and south cross-section of West Hill, along 
a line about a quarter of a mile from the Des Moines river. The 
best ash sections are near the corner of Crocker street; and the 
formation is locally christened for brevity the Crocker Ash-bed. 
The vertical section displayed at Crocker Corner is as follows : 
7. Soil, black loamy — — — .»Feet 2 
6. Till, yellow, bouldery, (Wisconsin) — „Feet 10 
5. Sand, very fine, gray (volcanic ash) — ._„__Feet 1 
4. Foam, black, pebbleless — __ — - — Feet 1 
3. Loess, yellow (Peorian) — Feet 15 
2. Till, dark red, bouldery (Kansan) — Feet 6 
1. Shale, variegated (Carbonic) exposed — — ___Feet 4 
The bed of the volcanic ash lies mainly in a shallow depression 
in the top of the loess. It is much disturbed and broken, a feature 
probably due to the plowing action of the Wisconsin ice. On the 
same horizon a few rods away is a bed of coarse gravel and small 
