448 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



According to the usual methods of interpretation the last-described 

 ridge is an esker. At its southeast end, near Boyd's residence, in western 

 Brady Township, it terminates in a gravel plain. Along the north side of 

 the esker are marshes and gravelly knolls and ridges associated in morainic 

 fashion; south of it are highland tracts on which there is scarcely any 

 drift. The height of this ridge and of the associated knolls and ridges on 

 its north side is scarcely 20 feet, with the exception of one knoll just north 

 of Mr. Boyd's residence, which is about 50 feet liigli. The large ridge 

 northeast of this esker, mentioned first in Lewis'? description, may have a 

 rock nucleus, there being on its north slope slight outcrops of sandstone 

 which appear to be in situ; one of them has a continuous horizontal 

 exposure of fully 20 feet. There are associated with this several loose 

 blocks of sandstone. The esker and accompanying knolls and ridges 

 occupy a lowland tract south of Slippery Rock Creek, into which the ice 

 sheet projected slightly beyond the regular border line, the boundary being 

 nearly a north-to-south line on its east side and an east-to-west line on its 

 south side. These features are such as Lewis and Wright have considered 

 morainic in adjacent districts on the west and north, and it is not apparent 

 why they should consider them extramorainic here. The presence of short 

 ridges of an esker type is quite characteristic of the moraine for several 

 miles to the north from this so-called extramorainic belt, and there is much 

 more assorted material than till in the knolls and ridges. This gravelly 

 portion was included by Lewis and Wright in the moraine. They also 

 included a gravelly portion of the moraine to the west near Rose Point, in 

 which there is little, if any, till, the basins and lower lands, as well as the 

 knolls and ridges, being underlain by gravel. 



La the northern part of Newcastle, on uplands standing 120 feet more 

 or less above the Shenango Valley, there is a winding gravel ridge, probably 

 allied to the eskers. It is about one-half mile long, 12 to 15 feet high, and 

 6 to 8 rods wide. Taken as a whole, its trend is N. 60° W. to S. 60° E., or 

 nearly in line with the striation in that vicinity, which is S. 45° E., but in 

 its windings it has variations from a north-south to a nearly east-west 

 course. Its structure is jaeculiar, there being a capping of till 3 to 5 feet 

 thick above a nucleus of assorted material. It is very seldom that eskers 

 carry a till capping, gravel usually being found on the surface as well as 

 below, but the ridge apparently belongs to this class of formations. The 

 till which caps it was ^jerhaps englacial material. 



