162 
IOWA ACADEMY OP SCIENCE 
At 107 feet from the surface the grayish blue clay contained traces 
of a brownish sand, the largest grain of which was a greenstone l-8xl-8x 
1-16 inch. A foot deeper (at 108 feet) several sub-angular pebbles of 
greenstone were encountered, one, the largest, 3-4xl-2x3-8 inch; another 
l-2x3-8xl-8 inch ; another 3-4xl-2x3-8 inch and sub-angular in shape. 
For the next two feet (108 and 109) the dark grayish clay was streaked 
with brown sand and contained minute pebbles, the largest of which 
was a chert 3-8x5-16x1-2 inch. The next half foot was a grayish clay 
with streaks of brown sand, and with gravel at its base. Within the 
next few inches came a bed of gravel, described as follows : 
GRAVE!. FROM SUB-AFTONIAN (.NEBRASKAN) DRIFT 1 FOOT. 
The gravel was coarse above, hue below, with half inch streak of 
bright red clay in the midst of it. 
The greenstone of the gravel were rounded and sub-angular, all smooth 
and unweathered, four striated, cue especially flat and striated, on one 
side, rounded on the other ‘and pitted in three places, the edges and solid 
angles rounded and polished — a typical glacial pebble. One limestone 
fragment contained part of a shell like a fragment of Prodiictus muri- 
catiis, the index fossil of the Des iMoines formation. 
The complete analysis of this gravel is as follows, all excepting the 
veiw finest material being used in making the analysis; 
ANAT.YSIS OF GRAVEL FOUND AT THE BASE OF THE AFTONIAN 
(GRAVEL FROM SUB-AFTONTAN DRIFT) 
Limestone, gray, many angular, one with a fragment like 
Procluctus muricatus, the index fossil of the Des Moines 
formation. This is all to be classed as local material. 
and is possibly derived from the very stratum on which 
the gravel rests 
63 
18.4 
0 
Greenstone, four striated, many rounded and sub-angular. 
148 
44.1 
57.4 
Sandstone, gray (local) 
15 
4.4 
0 
Sandstone (not local) 
6 
1.8 
2.3 
Granite, all but four light colored 
29 
8.6 
11.3 
Quartz 
33 
9.8 
12.8 
Chert, brown 
• 15 
4.4 
5.9 
Chert, dark 
5 
1.5 
1.9 
Chert, light ) 
4 
1.2 
1.5 
Quartzite, pink 
2 
.6 
.8 
Quartzite dark 
3 
.9 
1.1 
Quartzite, light 
7 
2.1 
2.7 
Schistose rocks 
6 
1.8 
2.3 
336, 99.6 100. 
