LASALLE COUNTY. 39 



NOTES ON LA SALLE COUNTY. 



LaSalle is one of the most interesting counties in the State, not 

 only from the variety and economic value of its mineral resources, 

 but also from the peculiar geological phenomena that are presented 

 within its borders. Situated on the northern confines of the great 

 coal field of Illinois, its coal products find a ready market in the 

 more northerly portions of this and the adjoining States of Wiscon- 

 sin and Minnesota, where no productive coal beds have hitherto been 

 found, and its favorable position in regard to the iron and zinc de- 

 posits of the northwest makes this county an eligible location for 

 the economical reduction of these metallic products. 



Among the economical resources of this county, bituminous coal 

 .ranks first in importance, and is found underlying nearly all that 

 portion of the county lying south of the Illinois river, as well as a 

 limited area north of that stream. Four coal seams, of sufficient 

 thickness to be of practical value in the production of coal, outcrop 

 within the limits of the county, and are the representatives of coals 

 numbered 2, 4, 5 and 7 of the general section of the Coal Measures 

 of this State. 



Their aggregate thickness is about sixteen feet, and their range 

 from two to seven feet, and they will be described further on in in- 

 dicating the localities where they are worked. 



An anticlinal axis crosses this county from northwest to southeast, 

 having its center in the valley of the Illinois river, about three 

 miles east of the city of LaSalle, where the Lower Magnesian lime- 

 stone of Owen, the oldest rock in the State, is elevated above the 

 surface to the height of about 80 feet. The Lower Carboniferous, 

 Devonian and Upper Silurian formations are all absent in this por- 

 tion of the State, so that the Coal Measures 'in LaSalle county 

 overlie, unconformably, both the Trenton limestone and St. Peters 

 sandstone of the Lower Silurian series. 



The exposure of the Lower Magnesian limestone is restricted to' 

 a limited area in the valley of the Illinois, its outcrop only extend- 

 ing eastward from Split-rock [about two miles. It affords the best 

 hydraulic limestone in the State, and the manufacture of hydraulic 

 cement has been an important industry at Utica for many years. 



The St. Peters sandstone, which immediately overlays the Lower 

 Magnesian limestone, forms the main portion of the river bluffs from 

 near Utica to a point two or three miles east of Ottawa, and on Fox 



