MAIN MORAINIC SYSTEM IN THE GRAND RIVER LOBE. 445 



parts of the uplands, cousistiiig of sharp hillocks and ridges 10 to 25 feet in 

 height, among which shallow basins are inclosed. 



In Little Brokenstraw Valley the inner (north) border of the moraine 

 is about as sharph- defined as on the Conewango. The valley, which is 

 comparatively open for some miles above the moraine, is so filled where the 

 moraine crosses that the stream in making its passage through winds about 

 among the drift ridges. The height of the most prominent knolls and ridges 

 is about 40 feet, but the majority have a height of only 20 to 26 feet. This 

 valley was not examined below the moraine, hence no data can be furnished 

 concerning its terraces. 



The best display of morainic topography along Big Brokenstraw Creek 

 is found south of Spring Creek station. For a mile or so south and south- 

 west of this station the valley bottom presents a very diversified surface, 

 there being hummocks and basins, ridges and sloughs, with sharp oscilla- 

 tions of 10 to 25 feet. The ice here, as in Jacksons Run, probably over- 

 hung, if it did not rest upon, the drift knolls, and determined the peculiar 

 form which they exhibit. 



Not only is there morainic topography in Oil Creek Valley for 2 miles 

 below Lewis and Wright's boundary line, but there is abundance of till on 

 the slopes and uplands outside their boundary, immediately north of Hyde- 

 town, and sharp drift knolls along McLaughlin Creek. The boundary 

 should, therefore, be located along a nearh' direct line across the valley 

 from the uplands northeast to those west of Hydetown. The head of the 

 terrace at Hydetown is 60 to 75 feet above the creek and slightly undula- 

 tory. The moraine rises only to a slight altitude above the head of the 

 terrace. It does not fill the valley so completely as it does the valleys in 

 Warren County, just mentioned. 



An interesting change in the rate of fall of the present stream in this 

 valle^^ near the outer border of the moraine, Avas noted by White.^ In a 

 distance of nearly 10 miles by course of stream from Centerville to Hyde- 

 town the fall is but 46 feet, while from Hydetown to Titusville, a distance 

 of 3f miles, the fall is 70 feet. This change of fall in the stream coincides 

 (juite closely with the outer border of the moraine, the rapid fall being 

 outside the moraine where the glacial waters formed an abruptly descend- 

 ing terrace, and the slow fall in the midst of the moraine where the channel 

 has been opened since the ice sheet withdrew. 



' Second Geol. Survey Pennsylvania, Kept. Q*, pp. 28-29. 



