220 GEOLOGY OF ILLINOIS. 



Analyses of a few coals from this county were made some years since, and 

 were published in the first volume of these Reports : since, fuller examinations 

 of the territory have shown the great variations in the character of the coal 

 within short distances, a phenomenon which usually accompanies outcrops so 

 near the edge of the basin, it has not been thought best to make any further 

 examinations of this sort. Throwing out the more noticeable impurities, such 

 as the nodules and layers of pyrite or " sulphur/' and the occasional bands of 

 slaty clay, the mass of the coal makes a very good article for steam purposes, 

 and some portions furnish a good blacksmithing coal ; but no considerable 

 quantity is found that appears suitable for smelting purposes. 



Assuming the coal area in this county to be about twenty square miles, and 

 allowing to the seam an average thickness of three feet three inches, the usual 

 rule of estimate would give 66,000,000 tons as the amount accessible within 

 the county. 



Building Stone. The quarries of Joliet and Lockport make no insignificant 

 figure in an estimate of the resources of Will county. The amount of stone 

 accessible here is almost unlimited. Only from twelve to fifteen feet of beds 

 furnishing " dimension stone " are now quarried, as the bottom of this brings 

 the quarrymen down to the water level, and the supply has thus far been so 

 abundant as to make deeper exploration unnecessary. Above the layers which 

 are quarried, there are several feet of beds, now decayed, which were originally 

 of very nearly the same consistency as the lower ones ; and when they shall be 

 worked back into the hill beyond the extent of atmospheric influences, will 

 probably be found equally valuable. The stone itself is a very compact, fine 

 grained, clinking, magnesian limestone, but thin seams of greenish clay run 

 irregularly through the whole mass, which, upon long exposure in situations 

 alternately wet and dry, must ultimately cause the most solid layers to split up, 

 especially when they are set up on edge. The separation in the quarry into 

 "ledges" of ten, twenty-four, thirty, and forty inches in thickness, simply re- 

 sults from the presence of somewhat thicker partings of this same greenish 

 shaly clay. It is not probable that this structure will sensibly affect the stone 

 used in building in ordinary situations, except after the lapse of many years ; 

 but care should be taken to reject such portions of the layers as come from very 

 near the outcrop. 



These beds were formerly described as composed of light buff stone, while 

 the deeper portions of the quarries now furnish " blue stone." The difference 

 results from the difference in amount of oxidation of the small portion of iron 

 disseminated through the whole mass, the change having resulted from atmos- 

 pheric influence. The same change must ultimately take place in all the " blue 

 stone" which is brought to the surface. 



The same beds are now quarried at Twelve-Mile Grove, in the town of Wai- 



