BY THE ROCKY WALL. 63 



the strata are composed of lamince which run obliquely across 

 the stratum. This is oblique lamination. It is of the same 

 nature as we saw in the semi-stratified drift. We concluded 

 that such mode of arrangement was caused by torrential 

 action. A similar explanation is allowable here, but the 

 water was less turbulent; it was, perhaps, wave action along 

 a beach. 



At Watkins' Glen, at the south end of Seneca Lake, is a 

 wild, deep gorge cut by a stream which rushes down from 

 the highland on its way to the lake. It is a striking example 

 of erosion, and the materials carried away are deposited in 

 Seneca Lake. The rocks here are shales. They are thin- 

 bedded, and soft enough to be cut with a knife. We see no 

 oblique lamination. This is a fine example of another sort of 

 strata. At Rochester, where the Central Railroad crosses the 

 Genesee river, a few rods above the Falls, we look down into 

 a gorge eroded by the river. The high walls of the gorge are 

 distinctly stratified ; and here many of the strata are com- 

 posed of limestone. No traces of oblique lamination can be 

 found in limestones. If we go to Portland, in Connecticut, 

 we may look down into wide and deep excavations in a sand- 

 stone rock of a brownish color, and very evenly bedded. 

 Near Cleveland, and at Berea, Ohio, are extensive quarries in a 

 grayish and bluish gray sort of sandstone. At Cincinnati, 

 back of the city, we find a steep slope formed of beds of lime- 

 stone, shale, and clay. Descending the Mississippi from St. 

 Paul to St. Louis, we see high cliffs of buffish strata overlook- 

 ing the river at frequent intervals now on the west, now on 

 the east. At St. Paul the rocks are distinctly stratified lime- 

 stone. At Davenport and St. Louis we find other kinds of 

 limestones. 



Now, I have directed your attention to these few exam- 

 ples out of hundreds for the purpose of enabling you to un- 

 derstand that everywhere solid rocks underlie the Drift; and 

 that they are, at least very generally, stratified rocks, and are 

 composed chiefly of sandstones, limestones, and shales. Let 

 us consider how these solid strata have been produced. None 



