GEOIvOGY OF IvA SALIvE COUNTY. 



31 



the west, and for about a half mile sinks g-entl}^ in that 

 direction, and then suddenly plung-es down at an angfle 

 of 40 ^ with the horizon, beneath the St. Peters. On 

 the west side of the ridg-e thus formed we find the 

 Trenton restino- on the St. Peters, and the coal meas- 

 ures, at first very thin, but thickening- very rapidly 

 toward the west, lyinw- on the Trenton. 



If now we look across the Illinois river toward 

 the south we shall see a point of rock similar to that 

 throug-h which the tunnel is cut, and we may, if 

 we will, follow the line of this sudden drop of the 

 strata to the south, finding- that the entrance to Deer 

 Park canon is a point in it, Lowell another, and that it 

 pursues a south, southeast, north, northwest course, 

 and that here once existed a considerable ridg-e, perhaps 

 a rang-e of low mountains. It is not easy to decide 

 whether the coal measures covered this ridg-e in all its 

 parts or not. We, however, believe that the}^ did not 

 cover that part of it north of the Illinois valley- 

 and between the tunnel and Utica station, and extend- 

 ing- north as far as the coal measures exist. This 

 ridg-e is disting-uished by the moderate dip to the east 

 or southeast of the strata on the east side of it, 

 and for the steep inclination to the west of those on its 

 west side. Along- the axis the rocks are much broken 

 up, and traces of the disturbance exist miles to 

 the east; but all the inequalities which we find in the 

 various strata must not be chargfed to the disturbance 

 caused by the formation of this fold. The movement 

 was certainh^ long- continued and produced very con- 

 siderable eifects. A part of it involved the coal meas- 

 ures, and it would seem that the principal part of the 

 chang-e occurred after all of our coal beds were formed. 

 It would not be eas}^ to explain the phenomena on the 

 Vermillion on anv other theory. The wrinkling of the 



