56 
IOWA ACADEMY OP SCIENCES. 
Under the action of weathering this lower blue clay became 
distinguishable too, by reason of its smoothness of surface, 
from the upper blue clay, the face of which it has been already 
stated is covered with rough right-angled projections. 
This difference would seem to be caused by a greater propor- 
tion of sand in the lower clay, which may be seen by close 
inspection to be the case. 
Thus, while weathering dims the attractive colors, while it 
mutilates and must soon destroy the exposure, its immediate 
effect is to reveal stratification and texture that in the fresh 
surface of the glacial section are sometimes concealed. 
This lower blue clay also shows a liberal number of angular 
fragments of limestone, one being observed which was a foot 
square and three inches thick. The entire bed, too, is found to 
be strongly impregnated with lime. 
Fragments of wood are abundant throughout this four feet 
of sandy clay with its mixture of lime. Though the wood is 
fairly uniform in distribution in the different parts of the 
stratum, there seems to be no observable system in its dis- 
tribution, no definite forest bed corresponding to the numerous 
instances given by McGee. This would seem to indicate that 
these woody fragments had been borne in from elsewhere rather 
than overwhelmed in situ. 
The woody remains consist of stumps, trunks, branches and 
twigs. Such short roots are found only as remain attached to 
the stumps. The tree trunks are most frequently in a hori- 
zontal position, and in that case are fl.attened out of the cylin- 
drical, thus showing the effects of pressure from above, since 
the vertical diameter is the shorter one. The maximum thick- 
ness of the trunks observed was eight inches, in a much 
decayed specimen. The length was uncertain. Preservation 
of the bark was observed in very few instances. 
Nearly all the specimens found appear to belong to the same 
species. Its lines of growth are very close together, an indica- 
tion that it grew slowly. It is apparently some soft wood. 
All of the wood when found was saturated with water, which 
dried out very slowly on exposure to the air. 
Though wood is found in both strata of the blue clay, fifty 
fragments may be found in the lower to one in the upper. 
Besides, the fragments in the lower bed are by far the larger. 
It seems worthy of notice that the lower blue clay was 
deposited so evenly over the undulating sides as well as the 
