38 GEOLOGY OF ILLINOIS. 



are not as easily worked as the rock from the overlying beds. A portion of the 

 material for the construction of the new public school building at Pittsfield, 

 which is one of the finest in the State, and reflects the highest credit on the 

 people of that town, was brought from Joliet, while the same bed of limestone, 

 affording a material in every way equal to that from Joliet, outcrops within ten 

 miles of Pittsfield. A want of the knowledge of this single fact, has probably 

 cost the citizens of Pike county far more than their proportion of the entire 

 cost of the Geological Survey of the State. 



The Burlington limestone, which outcrops over a wide area in this county, 

 will furnish an unlimited supply of excellent building stone. The thickness of 

 this formation is probably not less than one hundred and fifty feet, and nearly 

 the whole of it may be made available, either as a building stone, or, if the beds 

 are full of flinty material, as is locally the case, as an excellent macadamizing 

 material for the construction of turnpike or common roads. The rock is usu- 

 ally a light gray or brown sub-crystalline limestone, and where free from flint 

 or chert, is easily dressed and stands exposure well, being but slightly affected 

 by atmospheric action. In the vicinity of Montezuma, the lower ten feet of 

 the limestone exposed in the bluffs at that point, is a massive gray rock, quite 

 free from chert, and this lower division would afford dimension stone of any de- 

 sirable size. Similar beds are exposed on Big Blue creek, four miles southeast 

 of Pittsfield, where most of the rock required for use in the town is obtained. 

 There is about forty feet in thickness of the rock exposed here, mostly in mas- 

 sive beds, from two to four feet thick. On the west side of the county, it forms 

 an almost continuous outcrop, from ten to forty feet in thickness, along the 

 river bluffs, from the north line of the county to a point about two miles below 

 Atlas, where it is cut off by the elevation of the Upper Silurian strata, and on 

 the east side it forms a continuous outcrop in the bluffs of the Illinois, from the 

 vicinity of Griggsville Landing, to the south line of the county. It also out- 

 crops extensively on Bay creek, and all the smaller streams in the southern 

 part of the county. This renders it easily accessible to all that part of the 

 county south of Pittsfield, as well as the region adjacent to the river bluffs. 



The lower portion of the Keokuk limestone, which immediately overlies the 

 Burlington, is quite similar in character and appearance to the latter rock, and 

 furnishes a building stone fully equal to that afforded by the Burlington lime- 

 stone. It is usually rather free from chert at the principal points, where we 

 found it well exposed, and excellent building stone is obtained at the quarries 

 two miles north of Griggsville, on the south fork of McGee's creek. It differs 

 from the Burlington rock more in color than in texture, being usually more in- 

 clined to a bluish gray, but is semi-crystalline and highly crinoidal, being 

 almost entirely composed of the joints and plates of crinoids, cemented together 

 by a calcareous paste. The bands of shale, or marly clay, which are usually 



