144 



EUGENE WESLEY SHAW 



original upper surface. At over one hundred places the upper 

 limit of gravel has been determined by level, and that limit is in all 

 cases very nearly 300 feet above present low water. The eleva- 

 tion of the rock floor beneath the deposits has also been determined 

 at many points, and is found to be a little less than 200 feet above 

 the present position of the rivers. Thus, the upper limit of gravel 



TABLE SHOWING ELEVATIONS OF HIGH TERRACES IN WESTERN 



PENNSYLVANIA 



Place 



Upper Limit 



of Gravel 

 above Pres- 

 ent Stream 



Foxburg quadrangle 



*One mile north of Callens- 



burg 



*Turniphole 



Mouth of Clarion River .... 



Mouth of Bear Run 



Monterey 



Kittanning quadrangle 



Redbank 



Ford City 



New Kensington quadrangle 



Tarentum 



Carnegie quadrangle 



Allegheny 



Beaver quadrangle 



Beaver . -. 



Latrobe quadrangle 



*One mi'le northeast of 



Blairsville 



B urgettstown quadrangle 



*One and one-half miles 

 northeast of Burgettstown 



230 

 240 



304 

 305 

 308 



290 

 262 + 



275 + 

 300+ 

 306 



160 



*Gravel of local derivation (not glacial). 



falls regularly from 1,145 f ee t at Foxburg to 1,010 feet at Pitts- 

 burgh; the rock floor beneath the gravel from 1,015 to about 880 

 feet, and the river from 845 to 700 feet. Here, then, are three 

 approximately parallel planes, each of which slopes about 140 

 feet in 80 miles. In other words, the gravel formation holds its 

 thickness of about 125 feet, and slopes in the direction of present 

 stream flow. See table. 



The pebbles are well rounded, and lie in a matrix of sand and 



