224 
IOWA ACADEMY OF SCIENCE 
irregularity and lack of homogeneity in the materials laid down by the 
ice. Always and everywhere the principal ingredient of the Kansan 
drift is a joint clay — a clay that crumbles into small angular fragments 
when crushed in the fingers, and cracks in drying. It may be dark 
blue, or it may be leached out to a light yellow-brown, it may contain 
pebbles and bowlders, or may be free from them, lime-nodules may be 
present or absent, but without exception the clay shows the “jointed”' 
character. This peculiarity is distinctive. 
On traveling over the county, and observing the character of the 
surface deposits, one notices that scattered small bowlders and pebbles 
are much in evidence. Angular fragments of quartzite are particularly 
common. Every now and then, however, one gets into an area where 
the surface soil is free from stones of any sort, or practically so. This 
boulderless and pebbleless soil is, like the deeper drift, a joint clay. 
It is leached to precisely the same color as the superficial bowlder-bear- 
ing Kansan till on either side of it. It differs from the latter in no 
discoverable particular, except in the fact that it is free from bowlders 
and pebbles. It may occur at any level, and be of any extent. Some- 
times it covers an area but a few yards square; sometimes one may ob- 
serve it along the roadside for a mile at a stretch. It occurs on the 
crest of the divide at Greenfield, Grove Center and Adair. It also is 
found in the valley of Middle River at Howe, and near the county line, 
and in the valley of the Nodaway from Bridgewater down to the county 
line. It is scattered widely, is discontinuous, and one can never pre- 
dict where it will be found. At Greenfield it is twenty feet in thick- 
ness, at Grove Center four or five feet, and at Adair it reaches: a thick- 
ness of thirty feet or more. As has been said, its consistency is that of 
leached Kansan till. Wherever a section has cut deeply enough to 
penetrate both this deposit and the underlying bowlder-bearing Kansan, 
it is seen that there is no sharp line of demarkation between the two, 
but that the one shades off into the other. The bowlders and pebbles 
do not suddenly cease, as one follows the section upward, but they 
gradually become fewer and fewer. In fact a few small stones can al- 
most always be found in the deposit under discussion if one hunts for 
them. Sections at Greenfield, Grove Center and elsewhere show this 
gradual gradation of the bowlder-bearing into bowlderless clay. 
Finding a pebbleless and bowlderless clay scattered over the surface 
of the Kansan, one is at first inclined to conclude that it is a distinct 
formation, younger than the Kansan, and deposited on top of it. It 
is evident, however, that it cannot be of aqueous origin because of all ab- 
sence of stratification, and because of the wide variation in altitude cov- 
