148 Geology of Upper Illinois. 
bed up the ravine, until we ascend to the point B, on section 
twelve. Here we find a layer of coal two feet in thickness, form- 
ing the lowest part of the ravine, and traceable by means of a 
little gully descending from the east slope of the ravine, quite up 
to the level of the high prairie, a distance of eight or ten rods. In 
addition to this stratum, there shows itself at B, on the western 
slope of the Swanson ravine, and thirty feet above its bottom, a 
bed of coal four feet in thickness. Both the beds here described 
correspond, in direction and dip, with the main bed at the mouth 
of the ravine, nor can it admit of areasonable doubt that the up- 
per bed (whose thickness is four feet) is a continuation of the 
great deposit first mentioned. 
Still higher up, at C, where the ravine forks, the thick bed has 
been uncovered in two places, a few rods only apart. The coal 
here occupies the bottom of the valley, which, it must be under- 
stood, is situated at a level at least forty feet higher than at B. In 
the banks near the openings at C, occur frequent indications of the 
former combustion of the coal, in the abundance of brick-red 
slate and porcelain-jasper. Indeed it appears not improbable, that 
the entire ravine owes its origin to the inflammation of a body of 
coal near its out-crop, to which water, the exciting cause of com- 
bustion, must have found an easy access. _ In this way a channel 
may have been formed, which the spring freshets have widened 
and deepened, until the ravine has been brought to its present di- 
mensions. 
Among the loose materials accumulated against the edges of 
the strata in the upper part of the ravine, I observed an abundance 
of gypsum, in small white grains, resembling common salt, blended 
with argillo-marly soil; also frequent balls and kidney-shaped. 
masses of argillaceous iron-ore. 
Both branches of the ravine are shallow at C, and in running 
northward, soon attain the general level of the prairie; after 
which, the strata of course become concealed by the soil. But 
by taking the direction of the out-crop to the coal-bed, which is 
northwesterly, and proceeding a mile and a half across section 
- eleven upon section two, the sandstone which dips under the coal- 
bed of the Swanson ravine, reappears in slightly cohering strata; 
and still farther, by a distance of about half a mile, in the same 
course, at E, we strike the banks of the Little Vermilion, the east 
bluff of which, for some way, is composed of the identical grit of 
