GEOLOGY OE LA SALLE COUNTY. 



19 



At Marseilles the same coal is 40 feet below the 

 surface, and two miles west of Fox river it is resting- 

 on the St. Peter's sandstone, and 75 feet above the sur- 

 face of the Fox river bottom, or not less than 88 feet 

 above its level in the bottom, and 113 feet above its 

 horizon at Marseilles. West of the tunnel, lying- on 

 the St. Peters, we find a limestone which the fossils 

 found in it prove to be the Trenton. It is usually 

 a hard, semi-crystalline, somewhat silicious, g^ray to 

 buff gray rock, the upper strata thin, the low^er 

 thicker and more blue than g^ray. It is g-enerally trav- 

 ersed by veins of calcite, very white, sometimes trans- 

 lucent, and contains some cavities in part filled with 

 very handsome crystals of that mineral. On the south 

 side of the Illinois river, in the valle^^ of the Bigf Ver- 

 million river, it appears in several places, first about a 

 mile above Lowell, where the river has cut across a 

 ridg-e of it which extends to a point w^est of the bridg-e 

 at Lowell, next about the entrance to Deer Park. The 

 Economical Geology of Illinois, Vol. II, p. 233, near 

 the bottom, says: "The entrance to Deer Park is 

 throug^h the Trenton limestone, which forms portals 

 on both sides, until it abruptly terminates ag*ainst the 

 St. Peter's sandstone," etc. The Trenton does not 

 there or anywhere else in La Salle county terminate 

 abruptly ag-ainst anything*. The St. Peters sinks be- 

 neath it just as it does at the tunnel. There is no 

 fault, not even unconformability. A gfreat part of the 

 Trenton has been swept away, otherwise it w^ould add 

 a hundred feet or more to the heigfht of the park walls. 



Its next appearance is about 200 rods southwest 

 of Starved Rock, where it is very silicious. Here it 

 covers several acres. To the northeast of this, and 

 about eigfhtv rods southwest of Starved Rock, on the 

 edge of the bluff, are a few small mounds of it, and 



