BROADWAY MORAINE. 537 



simply an old course of the creek. The presence of the gravelly knolls 

 seems to oppose this idea and to show that the gravel tract was not 

 occupied by a stream after the ice had withdrawn, though it may have 

 been the course of the creek previous to the formation of the Broadway 

 moraine. It is thought that the ice sheet may have projected slightly 

 beyond the main ridge of the moraine and formed these knolls on the plain. 



Along Mill Creek there is not a conspicuous amount of gravel and 

 sand; on the contrary, its bluffs are usually composed of till and, with the 

 exception of a stretch embracing a few miles near its mouth, they stand 

 but a few feet above the flood plain of the stream. Near the mouth of the 

 creek at the crossing of the New California and Delaware roads, there are 

 rocky bluffs rising to a height of 60 feet above its bed, and the valley is 

 very narrow, scarcely 100 yards in width. Above the bluff of rock there 

 is a thin capping of drift, mainly clay, which does not show clear evidence 

 of fluvial action. 



Alum Creek, another stream leading southward from the outer border 

 of the moraine, is characterized for some miles below the moraine by a 

 narrow valley bordered by high bluffs of shale rising 80 feet or more above 

 the stream. Wherever the valley was crossed the shale is capped by till. 

 If there had been a discharge of glacial waters down the valley the stream 

 would apparently have been confined between the rocky bluffs of its 

 present narrow valley, which is even now occupied in places throughout 

 nearly its whole breadth by the creek. 



Aside from the fluvial phenomena noted, the outer border district 

 consists of a till plain, in which the number of "clay points" is fewer and 

 the proportion of "black ground" much greater than on the moraine. 



INNER BORDER PHENOMENA. 



There is, north of the Broadway moraine, an extensive district in which 

 the drift is comparatively thin (15 to 30 feet in general depth) and is com- 

 posed mainl}- of till. The surface is nearly all plane, and bowlders are less 

 conspicuous than on the moraine, but are not rare. Along Bokes Creek, a 

 western tributary of the Scioto flowing nearly parallel with the moraine and 

 less than 10 miles distant from it, there are in places slightly undulatory 

 tracts suggesting the marks of an ice margin, but there does not appear 

 to be a well-defined moraine. The valley of this creek is of interest, 



