NIAGARA FALLS AND VICINITY 87 



the rocks of this region have a gentle southward dip, which permits 

 the lower members to appear progressively as we proceed north- 

 ward over the surface of the old erosion plane. We may now pro- 

 ceed to describe the various members of this series in ascending 



order. 



Oswego sandstone 



This, the lowest member of the Siluric, is not exposed in the 

 Niagara region, as its point of outcrop is now covered by the waters 

 of Lake Ontario. (Sec sections i and 2, fig. 7) From borings, 

 however, we know its character and thickness, which in this region 

 is 75 feet. 



Medina sandstones and shales 



Only the upper portion of this formation is exposed in the 

 Niagara district, where the total thickness is more than 1200 feet. 



Red Medina shales. The upper beds of this division are the 

 lowest exposed beds in this region. They are bright red sandy 

 shales, generally of a very uniform character, though occasionally 

 a bed which might almost be called a sandstone occurs. Wherever 

 this rock is exposed to the atmosphere, it rapidly breaks down into 

 small angular fragments, which quickly form a debris slope or talus 

 at the foot of every clifif. In the faces of the older cliiTs this rock 

 is so friable, that it can readily be removed by the hand, the frag- 

 ments themselves being easily crushed between the fingers. In the 

 course of time these fragments disintegrate into a fine reddish clay 

 soil, which when wet has a rather tenacious character. 



As the lower part of the Niagara river from Lewiston to Lake 

 Ontario is wholly excavated in this rock, it may be seen wherever 

 the banks are kept fresh by the river, or where small lateral streams 

 enter the Niagara. Where erosion is not active, the shale bank is 

 soon reduced to a slope of red clayey soil, which generally becomes 

 covered with vegetation. 



A good place for the study of this shale is on the New York side 

 of the Lewiston suspension bridge, where a fresh cut reveals about 

 50 feet of the rock. The bridge is 65 feet above the river, and the 

 total thickness of red shale above the water at this point is therefore 

 115 feet. The shale here as elsewhere will be found to be seamed 



