236 GEOLOGY OF ILLINOIS. 



county. Soon after passing to the east of it the disturbance of the axis 

 referred to, appears. 



Almost the eutire area of the county belongs in the Coal Measures, 

 the exception being a small strip in the south-east part, equivalent to 

 about one and a half townships in area. The eastern boundary of the 

 Coal Measures within the county has been determined approximately. 

 Prof. F. H. Bradley traced the line iu Will and Kankakee counties; 

 in the latter, running south through the centre of the second tier of 

 sections east of the west line of that county to the south line of sec. 32, 

 T. 31 jST., R. 9 E., thence bearing a little west to the centre of sec. 32, T. 

 30 X., E. 9 E. No further evidence of it could be obtained without bor- 

 ing, and it was considered that a straight line from this latter point to 

 the rim of the basin — as determined at Chatsworth — would be a close 

 approximation to correctness. This would make the county line cross 

 the outcrop at the southeast corner of T. 29 K"., R. 8 E., and thence a 

 straight line to Chatsworth in the south-west half of sec. 4, T. 26 N., 

 R. 8 E. From thence, whether this line continues iu the same direction 

 to the south line of the county, or whether it bears eastward, is yet 

 unknown. Some indications of the northern boundary of the Coal 

 Measures iu Iroquois county favors the latter supposition. 



The general character of the surface of the county is rolling prairie 

 and very little broken along theVermilion river, which, with its branches, 

 is fringed with timber. The south-east part of the county is quite high 

 land. From four to six miles south of the county line, in Ford county, 

 about the centre of T. 24 N., R. 7 E., is the highest land of this region, 

 and the Illinois Vermilion, the "Wabash Vermilion, the Mackinaw and 

 Sangamon rivers all have their sources here near together. 



East of and parallel with the Vermilion is a ridge which may be 

 traced from a point west of Chatsworth, north-westerly into LaSalle 

 county, into T. 32 N., R. 3 E. This is gravelly and sandy, giving it a 

 distinctive character, as compared with the adjacent prairie. 



Drift. — The drift of this county is very variable and thinnest in the 

 uorth-west part of the county — in the vicinity of the Vermilion, and 

 throughout the course of this stream it is much thinner than away from 

 it on either side. At Pontiac, in the north part of the town, it is 

 eighteen feet ; at Fairbury and vicinity it is from a few feet to ninety 

 feet ; at Odell, Matson's boring reported it two hundred feet to sand 

 and water, and three hundred and fifty feet to rock, showing a great 

 depth of drift. Wells there have a very unequal supply of water. 

 Some iD town get abundance at five to ten feet, others fail to get water 

 at one hundred feet. Iu two borings water was obtained at about 

 ninety-five feet in gravel, while others got none, showing that the two 

 gravel beds so general in LaSalle county furnishing water, have run 



