230 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



fresh that only a glance is necessary to determine their class. As the 

 upland portion of this old drift is a thin deposit, it is usually deeply 

 weathered from top to bottom. In the valley portion weathering is very 

 pronounced to a depth of 20 feet or more. Usually the weathering extends 

 to the bottom of the coarse surface portion. 



Striated stones are common in the upland drift, and a few have been 

 found in the drift along the valleys. The markings are rather indistinct 

 because of weathering, and contrast strongly with the fresh lines to be seen 

 on rocks belonging to the Wisconsin drift. 



The records of a few well boring-s and some detailed observations are 

 here given, which throw light upon the thickness and structure of drift in a 

 few of the valleys. 



At Clarendon, near the present divide in the lowland that connects the 

 headwater portion of the Tionesta with the Allegheny, one well is reported 

 to have reached a depth of 240 feet below the level of the railway station 

 before entering rock. There were thin beds of stony clay and gravelly 

 material interbedded with heavy deposits of blue silt. Some wells in the 

 village enter rock at much less depth, but they are near the border of the 

 old valley. On the borders of the valley, in the vicinity of Clarendon, 

 glacial deposits occur up to a level fully 1 00 feet above the railway station, 

 or 1,500 feet above tide. These deposits on the border of the valley are 

 coarser than those below the level of the railway station; they include con- 

 siderable cobble and coarse gravel, but they contain only small bowlders, 

 none being observed which exceed 7 inches in diameter. The Canadian 

 rocks are so rare that search is often necessary to discover them. 



On the east side of the Conewango River, opposite Warren, very stony 

 or gravelly drift abounds up to fully 1,400 feet above tide, or to about 250 

 feet above the river. Wells indicate that the depth near the valley border 

 is often more than 100 feet, and it is probable that the middle of the valley 

 received a filling of nearly 300 feet. Only narrow remnants are preserved 

 on the valley borders, and these consist largely of gravel or very stony drift. 



In the valley bottoms near Warren there is a gravel deposit of Wis- 

 consin age, connecting with the moraine a few miles north of Warren, 

 which is composed of markedly fresher material than that at high levels on 

 the valley borders. The old gravel appears also to underlie the Wisconsin. 

 About 1^ miles below Warren, on the south side of the Allegheny, there is 



