608 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



sbort lines, none of them exceeding a yard in length, while many are out 

 6 to 12 inches. A few of them are curved, with their convex side toward 

 the south. The best-defined curved striae are about 2 feet in length, and 

 their departure from a straight line within that distance is fully 2 inches. 



Grilbert reports an observation on West Sister Island, in Lake Erie, 

 showing still greater difiFerence in bearing, there being a general glaciation 

 S. 80° W., and a single observation of striation in a north-south direction 

 which he designates the "intersecting series."^ He considers the southward 

 striation merely a local feature formed by the retiring glacier at a time 

 subsequent to the heavy glaciation, the striae being parallel to a steep bluff 

 over which the older grooves rise obliquely. 



Still greater divergencies were noted by W H. Sherzer in southeastern 

 Michigan,- the range being from about S. 6° W. to N. 20° W., or 154°. In 

 that region a southwestward movement was followed by a northwestward one. 



Wincliell has reported cross striae in Seneca Township, Seneca County, 

 Ohio, in which the older set bear S. 5° E. and the later and intersecting 

 series S. 23° W. 



Chamberlin has called attention to the disniptive crescentic gougis 

 displayed in the surface of the quarries at West Amherst,^ whose concave 

 side is turned toward the point of origin of the ice movement. Crescentic 

 cracks of this class he considers the natural result of a movement in 

 which the gouging agent is master of the situation. The "chatter marks" 

 displayed in many striated ledges in other districts resemble these crescentic 

 cracks in frequently having the form of a crescent, but they have their 

 convex side toward the origin of the ice movement. These Chamberlin 

 regards as the result of a movement in which the gouging agent is not the 

 master of the situation, but is dragged across the rock ledges. 



The remarkable phases of glacial action on the islands of the western 

 end of Lake Erie and in Marblehead Peninsula have been so well described 

 by Gilbert, Chamberlin, Wright, and others that further remarks concerning 

 them seem unnecessary. Plate XVII furnishes two illustrations of heavy 

 glaciation. The movement across these islands which produced the grooves 

 and striae was perhaps a late one, when the ice had only the Maumee 

 Basin in which to deploy. There are several striated exposures in northern 



1 Geology of Ohio, Vol. I, pp. 538, 539. 



2 Geol. Survey Michigan, Vol. VII, 1900, pp. 128-132. 

 ' Seventh Ann. Rept. U. S. Geol. Survey, pp. 219, 220. 



