AGE OP TERRACE SOUTH OF DES MOINES 
235 
portion of the ground moraine of the Kansan diuft sheet. The 
washed material from this source may be traced down along 
the floors of the ravines toward the lowland. Beneath this sur- 
face deposit along the sides of the river valleys water-bearing 
sands are found universally. Inspection of excavations for a 
tunnel at the Des Moines water works revealed no perceptible 
plane of separation in the sand; and inquiry at the Valley Junc- 
tion pumping station likewise brought no evidence of a plane 
of separation in the sand. At Carlisle there are numerous 
driven wells”, the sandpoints on the pipes resting in the sand 
at a depth of forty-two feet. At Avon the sand and gravel 
has been extensively excavated by the Chicago, Rock Island and 
Pacific Railway to ballast the lines to Allerton, to Indianola, 
and to Winterset. Here a test-boring is reported as giving con- 
tinuous sand and gravel to a depth of thirty feet below the 
surface of the terrace. Beneath this sand and gravel was found 
two feet of a blue clay without pebbles (silt?). Beneath the 
clay ‘‘quicksand” was found, but the depth of it was not as- 
certained. 
The sand as exposed in the excavations reveals stratification, 
and numerous pebbles up to an inch in diameter among which 
greenstones" are very abundant. One small feature observed 
in the gravel pit west of the railroad bears upon the question 
of climate. In a fresh exposure there was a small mass of brown- 
ish, unconsolidated sand about four inches in diameter, contain- 
ing a pebble of greenstone in the lower part of it; as if a small 
mass of frozen sand, with the lower portion weighted by the 
greenstone, had sunk to the bottom of the water. 
Aside from the record of the test-'boring at Avon but one 
other evidence was found of a division in the sand. A farmer 
reported that at his well on the edge of the upland there was a 
resistant, impervious stratum dividing the sand which his well 
penetrated. This condition part way up a ravine, though sug- 
gesting a division in the sand along the valley, may well exist 
while the sand along the vaUey forms one continuous deposit. 
The deposit of clay (silt?) over quicksand reported in the 
record of the test-boring, may easily have formed in the silting 
up of a valley. The gravel at the surface of the deposit is finer 
than that at a depth of six feet; and the gravel from the west 
3A complete analysis of the kinds of pebbles found in the gravel has not 
been made. In general appearance they look like any assemblage of pebblesr 
of equal size that has been washed from iKansan drift. 
