20 



GEOLOGY OF IvA SALINE COUNTY. 



then it is seen no more until we reach Covell creek. 

 Here it is found lyin^*- conformably on the St. Peters, 

 at the stone bridt>-e over that stream, on the river road. 

 It extends from the bridge about a half mile up the 

 stream, where it disappears beneath the coal measures, 

 has a breadth of about a half mile, and a thickness of 

 sixty feet or more. On the north side of the Illinois it 

 extends to just be3^ond the C. , R.I & P.R.R. tracks, not 

 reaching- the bluif . Here, as about Deer Park and near 

 Starved Rock, it appears to have been much disturbed, 

 and does not lie smoothly on the St. Peters, but forms 

 a series of little troughs and ridges, as if it had been 

 subjected to enormous pressure and forced into folds. 

 It also seems to fill a channel or trough in the St. 

 Peters, which on either side of it rises, like banks, 

 even with or above its surface. It appears nowhere 

 else in the Illinois valley in La Salle county. On Fox 

 river, however, there are several exposures, the first in 

 the southwest part of Mission township. Section 31, 

 and again in Section 18. The next locality known is 

 Section 36, Township 36, Range 5 East, and the next 

 is in Kendall county. Section 19, Tov\'nship 36, Range 

 6, East, known as Brad3^'s Quarry, where it i^- said to 

 dip 65 ^ north, a steeper inclination than any along the 

 Big Vermillion. 



The last and the most noted exposure of the Tren- 

 ton occurs on the Little Vermillion in Troy Grove 

 Township, near the village of that name. The extent 

 of the outcrop is not great. It can be traced a little 

 over a half mile one way, along the stream, and about 

 half as far at right angles to it, and the beds are about 

 twenty feet thick. It has been noted for the number, 

 size and fine condition of its fossils, in these respects 

 surpassing by far any other exposure in the county. 



