142 Geology of Upper Illinois. 
abundance, however, surpassed my expectation. They first at- 
tracted attention soon after leaving the twelve-mile house from 
Chicago, and appeared to form a belt between a quarter and half 
a mile in width, whose direction was north-west and south-east. 
In crossing this belt, it was uncommon to pass many rods with- 
out encountering a boulder. In general, they were rather more 
than half buried in the soil. They varied in diameter, from ten 
inches up to three feet, and belonged to the following species of 
rocks; granite, granitic gneiss, and trap. A few detached boul- 
ders only were noticed between this deposit and Ottawa. Soon 
after leaving this place, however, another band or patch of them 
was passed. 'They were here scattered over the Illinois bottoms 
so plentifully, as to prove objects of no inconsiderable annoyance 
in the road. 'T'wo miles below this locality, likewise, a number 
of large masses were seen, Others were occasionally met with 
south of this point, out upon the rolling prairie, in the direction 
of Vermilionville. What serves materially to heighten our inter- 
est in these boulders is, the consideration that they must have 
been transported over a distance of between two and three hun- 
dred miles, since the southern shore of Lake Superior is the neat- 
ont sonia Aadicg take H€4 sali chee in situ, 
Coal Formation. 
The northern boundary of the coal formation in Illinois, I can- 
not define with precision, not having been able to explore its lim- 
its in detail. As the result however, of inquiries from intelligent 
rsons and such observations as I was permitted to make in the 
region of the Illinois river, I am led to adopt the following as its 
general outline :—a line commencing just north of the mouth of 
the Kankakee and running west, across the Fox river, about eight 
miles north of Ottawa, and the Little Vermilion, five miles north 
of Rockwell. Whether it still continues without interruption, 
across the country to the mouth of Rock river, a distance of about 
one hundred miles, is uncertain. Coal is found on Green river, 
however, at a distance of twelve miles above where Rock river 
enters the Mississippi. It is possible, instead of thus crossing the 
elevated country to Rock river, that the border of the coal-field 
simply Sweeps round by Princeton, ten or fifteen miles west of 
pin and Henry, and then Seenaete the Illinois river at 
about the same distance from its western bank. From the mouth 
of the Kankakee, the coal passes off in a south-easterly direction 
