458 p. M. FOSHAY AND R. R. HICE GLACIAL GROOVES. 



direction, terminates by emptying into the Ohio river at Beaver. In its 

 course it receives but one large tributary, the Connoquenessing, which enters 

 it from the east at a point about thirteen miles from its mouth, and which 

 ordinarily carries about one-fourth the volume of water of the Beaver above 

 its point of meeting with the Connoquenessing. A more interesting region, 

 f )r its extent, to the student of Pleistocene geology can hardly be found. 

 Throughout its whole course the river flows in a valley deeply excavated in 

 the rocks of the Lower Productive Coal Measures and the Conglomerate 

 series (XII). For the first three miles of its course it lies wholly within the 

 drift-covered region, as do its parent streams. In the next two or three 

 miles it passes through the drift margin. The remainder of its course lies 

 in the driftless region, though the Pleistocene terraces are well developed in 

 many places along this latter portion. 



In topography the valley consists of a base-level plain, a mile or more in 

 width, bounded by slowly rising and rounded hills, and of a rock gorge, 200 

 yards in width, cut to a depth of about 350 feet in the floor of the upper and 

 wider valley, as shown in figure 1. The base-level plain is 250 feet above 



FiGURK 1. — Ideal Cross-Section of Beaver Valley. 



A, B = Base-level plain -,0,3 = Rock gorge; E, F = laner gorge; shaded portion represents 

 drift material and Pleistocene terraces. 



the river at its mouth and about 100 feet above water-level at Lawrence 

 Junction, a diflference of about 100 feet, while the level of the river has risen 

 somewhat less than 100 feet, so that the plain slopes slightly to the north- 

 ward. The plain is covered by a deposit of clay, sand and gravel, the first- 

 mentioned member being most characteristic, with a maximum observed thick- 

 ness of twenty feet. This deposit is older than the terminal moraine and the 

 kames of the second glacial epoch, as it is found underlying a large kame 

 at the mouth of the Connoquenessing. It probably represents the slack-water 

 sediments of the continental depression accompanying the first glacial epoch — 

 the Columbia period of McGee. 



The rock gorge for the eleven miles between Wampum and Beaver Falls 

 has almost perpendicular walls, and so forms a veritable caiion, the precipi- 

 tous sides being due to the remarkable development of the Homewood sand- 

 stone, which forms the top member of the canon walls as also of the Con- 

 glomerate series (XII) and is a very massive sandrock from 75 to 150 feet 

 in thickness for the whole distance. 



