The Columhid Formation in X. W. TlUnois. — Hershey. 9 
<Tops, although fairly numerous, never exceed more than a 
few feet in thickness. The typical localities are in the banks 
of Yellow and Ch-ane's creeks, a few miles west and south of 
the city of Freeport, but even here it can be examined only at 
low water. Wherever seen, it is in general a loose agglomer- 
ation of small gravel and sand of a blue gray color. The 
following section is typical of the deposit. It is commonly 
•overlain by bluish gray loess with few shells. 
1. Light blue-gray gravel and sand, with manj- shells, (i inches 
2. Dark blue-gray or bluish-brown fine sandy clay, full 
of black and light, brown bits of wood 12 inches 
3. Very loose light gray coarse gravel and sand, with 
shells and a little wood, exposed 8 inches 
Ustially the more sandy portions are full of shells of small 
size. A small collection of these has been submitted to Mr. 
C. T. Simpson, of the department of eonchology, in the Na- 
tional Museum, who reports the presence of the following 
species, all of which are found living abundantly in the fresh 
waters of northern Illinois to-day : 
Pleurocera subulare Lea. Plaiiorbis blcarinatus Say. 
Phj'sa heterostropha Say. Spluerium stamineum Con. 
Valvata tricarinala Say. Pisidium abditum Hald. 't 
These all differ from the fossil shells generally reported 
from the loess along the Mississippi river. 
The fossil vegetable matter is in the form of {a) small 
black particles of carbon disseminated through the deposit, 
and giving it its blue-gray color; (b) long thin fibers, appar- 
entl}'^ rootlets, many of which seem to be in situ in the dark 
sandy clays in which they now occur; (c) many black, semi- 
decayed pieces of tree branches, occasionally reaching a thick- 
ness of several inches. Some of this wood, from the same lo- 
cality as the foregoing shells, was submitted to Prof. F. H. 
Knowlton, who reports that the interior is too much damaged 
by pressure to permit determination of the species, but that it 
is apparently coniferous. Branches have been found which 
certainly belong to deciduous species, but most of the woody 
matter from this horizon appears to be of cedar and pine. 
The material of which this deposit is composed throws 
much light on the manner of its formation. At least nine- 
tenths of the pebbles in the gravel are of local material, 
principall}^ Galena limestone and white chert, derived proba- 
