472 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



even the elevated rock ridges of northwestern Pennsylvania having a suffi- 

 ciently compact till coating to make the soil cold and wet. In the valleys 

 of this district the di-ift is chiefly assorted material or a sandy till, as in the 

 moraine, and for this reason the valleys often contain drier ground than 

 the uplands. 



TERRACES. 



The Shenango Valley has at many points terrace-like benches 50 to 

 100 feet above the level of the creek, but these have not been carefully 

 worked out and correlated. They were noted at Big Bend, where the 

 height is about 50 feet above the stream; at Sharpsville, where it is about 

 90 feet, and below Newcastle, where two occur, one at 50 and another at 

 about 100 feet. White notes ^ terraces between Sharon and Newcastle whose 

 height is given as 20, 50, and 120 feet above the stream. As a rule these 

 terraces are built up in a previously eroded valley, but below Sharpsville a 

 terrace-like bench, 75 to 80 feet high, exists which has in part a rock plat- 

 form and in part a substratum of till, only the upper portion being assorted 

 material. This assorted material was evidently formed by a sti'eam, but 

 the head of the terrace has not been traced out. It is probable that careful 

 study of the terraces on this and other valleys will bring to light a relation- 

 ship between the streams which formed them and successive positions of the 

 margin of the retreating ice sheet. 



CORRELATION AND CHRONOLOGICAL POSITION. 



The number of moraines in the Grand River lobe is much smaller than 

 in any of the lobes farther west. The ClcA'cland and the Euclid morainic 

 belts extend west only about to Cleveland, hence the oxiter morainic system 

 and the fragmentary moraines between it and the Cleveland moraine are 

 the sole representatives of the whole series in western Ohio, a series com- 

 pi'ising not fewer than ten somewhat distinct moraines. 



The small number is attributable in jjart at least to the coalescence of 

 several moraines in the outer belt, and perhaps in part to an obliteration of 

 certain moraines by later advances. Specific correlations with each of the 

 moraines farther west are therefore scarcely to be expected. 



In the shelf or shoulder between the Scioto and the Grand River lobe 

 are two series of moraines, each comprising two or more members. The 



' Second Geol. Survey Pennsylvania, Eept. Q', p. 95. 



