The Cohinihid Foniidfion in JV". ]V. {Uinoitt. — Ilershey. 13 
Its constitution, distribution, stratification, and surface con- 
figuration, seem strongly to support the hypothesis that the 
brown sand division of the Valley loess was formed under flu- 
vio-lacustrine conditions, and that it consists of glacial silt 
derived from an ice-sheet somewhere to the east. 
The lower division of the Valley loess passes into the upper 
division by interstratification. This latter is essen^'ally a 
stratified fine sandy clay or silt, having usually either a light 
or dark bluish gra}^ color; but where it has been exposed to 
oxidation, it has a light buff (;olor. The lamination is very 
distinct in the lower portion, but becomes less so upward; 
and finally it totally disapj^ears at the top of the deposit. 
There is also a gradual decrease in the size of the particles 
from the base upward, and a general thinning of the strata to 
the west. A few fossil shells are sometimes found in this di- 
vision of the loess, apparently similar to those enclosed in the 
loess along the Mississippi river. Calcareous concretions are 
abundant in some localities, and the surface on exposure rap- 
idly becomes coated with a whitish eflfiorescence. When sub- 
ject to erosion, as in gutters and stream beds, the outcrop re- 
sembles laminated shales, sometimes having the appearance of 
being tilted at a high angle. At one place a small gully was 
found partially filled with rounded pebbles of a dark brown 
color, which, on examination, proved to be composed of loess 
belonging to this division. 
This upper or "blue cla}'^" division of the Valley loess is 
found everywhere (unless it has been removed by erosion) in 
the main valley of the Pecatonica river and along its princi- 
pal branches in Stephenson county and in a portion of Winne- 
bago county; but it occurs only to a limited hight above the 
flood-plain of the river at Freeport. It attains its greatest 
thickness, which is 20 feet or more, at levels less than f50 feet 
above this llood-plain ; and thence upward it rapidly thins out, 
totally disappearing before the 100-foot level is reached. 
Hence, although it has a rather wide distribution, it is essen- 
tially a valley loess. 
The phenomena connected with this division of the loess 
seem to indicate a formation under tluvio- lacustrine condi- 
tions similar to those of the lower division, but in a deeper and 
more extensive lake, with less powerful currents than that 
