1890.] . Geology and Paleontology. 1183 
It also sometimes occupies the surface of broad, shallow valleys 
which are in part filled with Valley Drift.? When this occurs, how- 
ever, it is shown to have been laid down at a period subsequent to that 
of the upland. 
This sheet, as seen developed in the region under consideration, is, 
for the greater part, of a quite homogeneous silt-like composition, of a 
grayish-black color, and attains an average thickness of from one to 
two feet. In places this formation contains well-rounded, smooth, and 
sometimes striated pebbles of Drift origin, and well-rounded, sometimes 
angular bowlderettes. At other times neither pebbles nor bowlderettes 
enter into this formation as component elements.’ 
The three following cuts will give a good idea of the stratigraphical 
relation which this formation sustains to the subjacent Drift, as well as 
give a conception of the relative nature of the lithological character of 
the two divisions. 
1-3. ehe of Transitional Drift and ee Drift, memet the relative 
epus and lithological character of the two formations. 
I. Section in road cut, in gently guess praiie region, six 
miles west of Charles City. The upper bed, which is two feet in thick- 
ness, represents the Transitional Drift, and is of a fine homogeneous 
composition, containing, so far as observed, neither pebbles nor bowl- 
derettes. This passes quite abruptly into the underlying gravelly Drift, 
which is one and one-half feet in thickness. The lower bed (nine inches 
thick) is fine siliceous sand. 
2. Section in road cut, about two miles north from Rockford, and 
three-fourths of a mile distant and more than one hundred feet (esti- 
mated) above the Shellrock River. The higher bed, a little more than 
two feet in thickness, is Transitional Drift, the lower part of which is 
slightly yellow, and contains some rounded pebbles. This passes 
quite rapidly into the coarse Drift gravel below. 
3. A general section of the two sheets under consideration. The 
upper deposit contains some pebbles and bowlderettes, and passes, 
more or less rapidly, into the underlying Drift or Till. This member 
2 This is well illustrated in Fig. 2 of the above-mentioned paper. 
3 We have observed this sheet well developed in portions of Southeastern Iowa. 
