2S2 GEOLOGY OF ILLINOIS. 



The rock is free from chert, and would afford an excellent material for 

 window caps and sills, as it cuts much more easily than the flue-grained 

 limestones below, and is also more uniform both in color and texture. 

 Most of the macadamizing material used in this county is obtained from 

 . the hard, bluish-gray limestones of this group. 



The lower or Warsaw division of this group is well exposed a half 

 mile east of Columbia, and some portions of it afford an excellent build- 

 ing stone. The upper portion consists of about twenty feet in thick- 

 ness of a light-gray, granular limestone, entirely free from chert, and 

 in heavy beds, some of which are from three to four feet thick. The 

 rock splits easily, affording dimension stone of any desired form and 

 size. This rock appears to dress well, and is really one of the best 

 building stones in the county. The lower beds of this division are 

 also partly heavy-bedded buff or brown limestones, partly magnesian 

 or dolomitic in structure, and afford a durable building stone. This 

 division of the group is well exposed in the river bluffs about a mile 

 and a half below Salt Lick Point, where it forms a bluff more than a 

 hundred feet in bight, nearly the whole of which is a valuable building 

 stone. The Keokuk group is not fully exposed in this county, except 

 along the river bluffs in the southwestern portion, where there has as 

 yet been but little demand for building stone, and no extensive qua r- 

 ries have so far been developed in it. The upper beds seen at Mr. 

 Pryor's place, a mile and a half east of Salt Lick Point, were in toler- 

 ably regular beds and comparatively free from chert. The lower sixty 

 feet of the section at the same point consisted of gray limestone, some- 

 what cherry, but similar to the limestones obtained from this group at 

 more northern localities. The Burlington limestone appears to be more 

 cherty at the outcrops seen in this county than it usually is in the 

 northern portion of the State, and consequently no great amount of 

 good building material may be expected from it. 



The entire thickness of the Trenton group might be made available, 

 if it was found at any point where a demand for building stone existed, 

 but as its only outcrop is in the river bluffs, remote from any town, its 

 supplies of useful building material are for the present only of prospec- 

 tive value. 



Marble. The Trenton limestone affords some beds of light-gray crys- 

 talline thick-bedded rock, that receives a fine polish, and the thickly 

 imbedded organic forms give to the polished surface a slightly mottled 

 appearance that is rather pleasing. This rock is extensively quarried 

 at Glencoe, in Missouri, and is known as the Glencoe marble. It may 

 be obtained at Salt Lick Point, in this county, in inexhaustible quan- 

 tities, and if railroad facilities were at hand would become a source of 

 considerable revenue to the county. 



