978 Glacial Drift of the Basin of Iowa. 
and one-half miles northwest from Rockford; on the east and 
west sides of Linn creek, one and one-half miles west of Rockford, 
and other places. These terraces appear to have been formed by 
the contracting and deepening of the channels of these streams by 
their own waters. 
The last recognized division of the later Glacial epoch is the 
Loess formation. This formation is represented by only a few 
limited outliers at different points along the course of the Cedar river. 
On the west side of the Cedar, at Mitchell, in Mitchell county, is 
a local deposit of very fine and homogeneous, typical yellow 
loess, having a thickness of twelve feet. This rests directly upon 
a layer (from four to six inches in thickness) of clean rounded 
and angular drift pebbles, and the pebbles in turn rest (in places) 
upon a very dark, ferruginous layer of rock, which lays upon 
broken-up Devonian limestone below. 
In the lower portion of the exposure of loess, one or two large shells 
was found, which were, however, in a too imperfect state of 
preservation for satisfactory determination. On the east side of the 
Cedar, one mile above Floyd, another outlier of this forma- 
tion occurs. The loess at this place is like that observed at 
Mitchell, except that it contains small quantities of silicious 
sand in places, and in places has a very slight blueish-gray shade. 
The greatest observed thickness of this exposure was, by estimate, 
twenty-one feet. No drift was seen to intervene between the 
loess and the coarse-grained calcareo-silicious sandstone below. 
The surface of the rock at this place rises to a height of over 
one hundred feet above the water in the Cedar. 
The locality where this formation is next observed is on the same 
stream, at Waverley, about thirty-two miles below Floyd. The 
loess here (so far as ascertained) is light yellow, fine-grained 
and homogeneous, but contains at one point a very large amount 
of dark, grayish-brown silicious sand. No fossils, concretions, OF 
ferruginous tubules was noticed in the loess of this place, ; 
Probably no department of geological investigation has greater 
’ This sandstone attains a thickness of two feet, and rests upon very 
hard and fine-grained, grayish-white Devonian limestone. No sand- 
stone exactly like this is known to occur at any other point in northern 
owa. i ; 
