GEOLOGY OF LA SALLE COUNTY. 



13 



dazzles and astonishes man, to be veiled the next 

 moment in eternal gloom. 



A look at the table of strata shows us that the 

 lowest formation in this count}^ is the calciferous or 

 Utica cement rock, the lowest member of the g-reat 

 Silurian era. It consists of thin bedded, 'blue rather 

 hard limestones with layers of very porous calcareous 

 sandstone and some beds of a hard, coarse sandstone 

 nearl}^ a foot thick. It forms the floor of the Illinois 

 Valley from a half mile east of Utica to near the tun- 

 nel west of that villag-e, a,nd the north bluff from 

 Utica to a fourth mile east of the tunnel, but does not 

 appear in the south bluff. 



The upper beds of this formation contain many 

 laro-e (18-inch to 3-feet diameter) chert nodules, made 

 up of concentric layers, often variously colored. These 

 are well shown in the bed of a small stream in the 

 northwest part of Utica villag-e, on the west side of the 

 road leading- by the cemetery up the bluff, just south 

 of where the road to the west leaves it. Below this 

 nodular bed thirt}" strata are found varying- in color, 

 thickness and composition in a total thickness of 83 

 feet 8 inches. The section beg-ins in^St. Peter's sand- 

 stone and descends less than half way throug-h the 

 calciferous. It was taken at a point about three- 

 fourths of a mile west of Utica station: 



