Glacial Drift of the Basin of Iowa. 977 
silicious sand, with a layer of coarse rounded gravel at the bottom, 
resting upon Devonian strata. The upper bed isa fine silt-like soil, 
mixed with coarse drift gravel, due in part to secondary accumulation 
arising from wash from a slight adjoining slope. The talus of 
sand at the base conceals several subordinate beds. 
Fig. 2, 
Fig. 2 represents a section of Valley drift near Nora Springs, illus- 
trating oblique stratification. The material is well rounded gravel and 
ii PEN R- pP 
sand. The upper bed isa black I g - g small 
drift pebbles. The second bed is a yellow clayey soil, with some fine 
gravel in the lower portion.! The next succeeding bed is partially 
stratified gravel and sand. The wave-like parts of Figure 1 cor- 
respond to succeeding plunges in the rapidly flowing waters, and 
indicates a much more turbulent condition of the water than when 
the material of Figure 2 was deposited. 
At Clarksville, in Butler county, and other places, the Valley 
drift is seen to be obliquely stratified, the same as near Nora Springs. 
The gravel of this division at different points has been more or less 
solidified by calcareous cement. An interesting feature of this 
formation is that very often a large percentage of the finer material 
occupies the lowest position. while the coarser material often occu- 
pies the higher position. 
Fine examples of terraces are observed along the streams of 
this region; for example, on the west side of the Cedar, a few 
miles above Waverly; on the west side of the Shellrock, two 
' These beds well illustrate the condition of the first few feet of the 
oe accumulation of nearly all parts of the area under considera- 
