244 GEOLOGY OF ILLINOIS. 



are the remnants of some broken up beds which may formerly have connected 

 that with the Illinois field. 



Both these beds and the lower member of the Drift formation give rise to 

 numerous springs, some of which have taken up so much lime from the lime- 

 stone pebbles which fill the gravel, that, upon coming to the surface, they make 

 abundant deposits of tufa, as along the bank of the Big Vermilion, at Danville, 

 and especially at the " Moss Bank" on North Fork, about one mile northwest 

 of that city. Some of the deposits are light and porous, and take beautiful 

 impressions of the mosses, twigs, and leaves which become imbedded in them. 

 Kecent snail-shells, thus fossilized, are not rare. In other cases, the deposition 

 has gone on more slowly, and without the introduction of extraneous matter, 

 and we find as the result some very solid masses with a radiating semi-crystal- 

 line structure, which approximates more nearly the ordinary stalagmitic for- 

 mations. 



The lower member of the Drift the (( boulder-clay" is a tough, light-blue 

 clay, filled with gravel of various degrees of fineness, with some larger boulders. 

 In this county, it is from fifty to eighty feet in thickness, and forms some con- 

 siderable bluffs, as at Mills'* s mill, on Middle Fork, where it is capped with the 

 gravel and sand of the upper member. It also forms the mound at Kyger's 

 mill, near the mouth of Grape creek. Here, the river ran for centuries to the 

 west of the mound, and excavated a broad valley, which is now deserted and 

 partially filled up, and the stream passes to the eastward, leaving a small island 

 of the boulder-clay, which presents an almost perpendicular face on the east 

 side, where it is now undermined by the current. Curiously enough, a spring 

 of cold water flows out at the top of this mound. 



Goal Measures. The rock formations of this county all belong to the Coal 

 Measures. The following is a general statement of the section, from the high- 

 est beds seen in the county to the junction of the Big Vermilion, with the 

 Wabash river below Eugene, with the addition of the section from the lowest 

 beds there seen to the bottom of the Lodi salt well, as carefully determined 

 and reported by John Collett, Esq., of Eugene. It was found necessary to 

 make these connections with the Indiana field, both in order to judge of the 

 beds underlying Vermilion county, and also to connect the section in Vermilion 

 with that in Edgar county : 



FEET. 



1. Light drab limestone , 12 to 18 



Level of coal No. 12 ? 



Covered ? 



2. Shaly sandstone, with some solid beds 25 to 50 



3. Olive, dark red and light blue clay shales, lower part sandy and micaceous, 



with bands of argillaceous limestone 5 "20 



4. Black shale " 3 



5. Coal, No. 11? " 1| 



