24S 
The American Geologist. 
October, 1894 
these quarries that I came across t he most conclusive evidence 
of erosion. 
The Cascade ravine is about half a mile in length and en- 
ters the Mississippi river at right angles. About one-fourth 
of a mile back from the mouth of the ravine these quarries 
occur. One of them is on the south hank and is situated on 
both sides of a short, hut deep lateral ravine, the bottom of 
which is several feet lower than the stratum of white lime- 
stone. In working off the corner between the main and lat- 
eral ravines the white limestone layer was found to he much 
eroded ami the blue shale was uniformly deposited directly 
Fig. 1. Unconformity of Upper Burlington Strvta. 
[The white patches in the shale are marks made by the cinarryman's pick. | 
upon the water- worn surface, and conforming to all of its ir- 
regularities and inequalities. The erosion is lateral more than 
vertical and the inequalities are quite abrupt, one bench 
amounting to fully two feet ; and vet the blue shale covers 
this without a break. The shale is itself capped with fairly 
well-bedded limestone. The contact of the shale with the 
limestone is well shown in the accompanying figure. 
This is direct evidence of erosion in the first half of the 
I'pper Burlington epoch. An interesting fact which necessa- 
rily follows is that the present system of drainage must have 
