Geology of Upper Tilinois. 141 
face of the prairie at Plainfield, nine miles from Juliet, and very 
abundantly also at this last place. 'The beds at Plainfield and 
Juliet, however, are not rich in fossils. 'The rock is quite close 
in its structure, and where acted on by the weather, of a yellow- 
ish buff color, much resembling the lithographic stone of Sohlen- 
hofen, in Bavaria. The quarries at Juliet, afford it in very even, 
distinctly stratified layers, whose position is nearly horizontal, 
their thickness being such as to render it a very valuable building 
material. I noticed one variety of the rock at this place, which 
had been thrown out in sinking a well, the appearance of which 
was very analogous to that of true dolomite, (the gurhofian va- 
riety.) Its color is a grayish white, with a tinge of green; 
throughout the masses were crevices and openings, whose walls 
were lined with transparent crystals of quartz. 
The magnesian limestone continues very abundantly in the 
bed of the Des Plaines, below Juliet, and recurs frequently on the 
road across the prairie to Holderman’s grove, twelve miles east of 
Ottawa; after which, no more rock was observed until I reached 
* the bed of Fox river, just above the village of Ottawa. At this 
point, we strike upon the coal formation. 
Of the existence of formations more recent than the magnesian 
limestone in this region, my own observation permits me to add 
nothing, beyond what has already been stated under the head of 
the lake shore near Chicago. By the kindness, however, of Mr. 
W. B. Ocpen, the mayor of Chicago, and Col. THornron, presi- 
dent of the board of commissioners for the canal, I am enabled to 
annex some additional particulars. 'The excavations for the ca- 
nal on the wet prairie give the following superficial formations: 
one to two feet, black vegetable mould, and two to six feet, yel- 
low, clayey loam, resting on blue clay. On reaching the Des 
Plaines, the sections give, in the first place, one foot of black 
mould ; secondly, four feet, yellow sandy clay; thirdly, one and 
a half feet clean black sand, and lastly, twelve feet “vegetable 
formations with shells.’* 
The occurrence of boulders in the rolling prairie had, often 
been mentioned to me, under the significant and original appel- 
lation, bestowed upon them in this region, of “lost rocks.” Their 
* From the same source, I learn that the magnesian limestone beneath these de- 
posits often abounds with vertical fissures, filled with clay, from one inch to sev- 
eral feet in breadth. 
