58 IOWA ACADEMY OF SCIENCES. 



CORRELATION OF CARBONIFEROUS FOtiMVTIONS OP THE OZARKS. 



SOME GEOLOGICAL FORMATIONS OF THE CAP-AU- 

 GRES UPLIFT. 



BY CHARLES R. KEYES. 



Cap au Gres is a name that was given by the early French 

 voyageurs to a prominent sandstone headland rising from the 

 east side of the Mississippi river a dozen miles above the 

 mouth of the Illinois. The point is of special interest geolog- 

 ically on account of having, side by side, beds of the earliest and 

 latest Paleozoic. The sandstone is Cambrian in age and the 

 contiguous limestone middle Carboniferous. The cliff marks 

 the position of the most profound dislocation, or fault, known 

 in the Mississippi valley. Near the line of the slip the hori- 

 zontal strata are abruptly bent upward at high angles, as much 

 as 80 degrees, immediately against the fault plane. (See plates 

 I and II). Hence it is that within the very short horizontal 

 distance of less than a mile the greater part of the entire Pale- 

 ozoic section of the region is well displayed. 



