112 GEOLOGY OF ILLINOIS. 



ties in the immediate vicinity of the railroads, is not less at the present time than 

 in the period of the early settlement of this region. The principal kinds of tim- 

 ber are, black, white, red and bur oaks, bitternut and shell-bark hickory, black- 

 walnut, butternut, elm, black and white ash, soft maple, sugar maple, and cot- 

 tonwood. The red cedar and a arbor vitse are also found in a few localities in 

 this district. The varieties of soil are altogether the same as have been des- 

 cribed in the reports on the adjoining counties on the prairie a deep, black or 

 dark brown humus, and in the timber a lighter colored, sandy clay soil or loam. 

 In a few localities the sandy or gravelly character of the soil is more predomi- 

 nant, as in township 42, ranges 6 and 7, in the northern part of Kane county, 

 where some of the ridges or irregular elevations of land, separating small wet 

 prairies or sloughs, are quite sandy. These low prairies are found, of incon- 

 siderable area, in various portions of the district, but are more abundant in this 

 particular region. Along some of the principal streams, and especially the Fox 

 river, in Kane county, the country is more roughly broken, and can in some 

 parts even be called hilly, although the more abrupt elevations seldom exceed 

 eighty or one hundred feet above their immediate base. 



The geological formations, otherthan the surface deposits of Alluvium, Drift, 

 etc., which appear at the surface in this district, comprise portions of the Niag- 

 ara, Cincinnati, and Trenton groups. The St. Peters sandstone, also, judging 

 from facts developed in the survey of LaSalle county, probably underlies a por- 

 tion of the southern part of DeKalb county, but as the whole of that region is 

 covered with heavy accumulations of Drift, no exposures of this formation are 

 to be found. The exposures of the older rocks are found only along the 

 courses of the larger streams, and at one or two isolated localities in DuPage 

 county, on the easternmost borders of the district. Elsewhere they are overlaid 

 with heavy deposits of Drift, varying from twenty to eighty or one hundred 

 feet in thickness, and in some localities even more. 



Above the Drift proper, we have only the surface soils and a few local allu- 

 vial deposits in the river bottoms, etc. Some of the springs along the upper 

 course of the Fox river, in Kane county, issuing from the lower limestone bed 

 of the Niagara group, hold much lime in solution, and deposit calcareous tufa. 

 A considerable deposit of this material occurs on the eastern bank of the river, 

 about three miles north of the city of Elgin, and close to the track of the Fox 

 River Valley railroad. This deposit was formerly quarried for the manufacture 

 of lime, and is exposed in the excavations to the depth of about four feet. It 

 appears to be regularly bedded, and varies in structure from a loosely compact- 

 ed, porous material, resembling petrified moss, and full of traces of vegetable 

 remains, to a compact travertin, almost resembling in density some of the older 

 rocks. The whole extent of this deposit is not to be seen, as it is covered by 



