138 THE GLACIAL LAKE AGASSIZ. 



granitic, of all sizes up to 5 feet in diameter or rarely larger. These 

 were probably combed out of the ice-sheet in its passage over this hill. 

 Comparatively few bowlders occur on the small flat area at its top. Pilot 

 Mound, an equally prominent hill seen from this in looking northwest, is, 

 like Star Mound, a knob of Cretaceous shale with thin covering of drift, 

 but it has no such unusual profusion of bowlders on its slopes. Rock 

 Lake, through 'which the Pembina flows, derives its name from the remark- 

 able abundance of bowlders, mostly granitic, up to 6 feet or more in 

 diameter, bordering its shores ; and along a distance of 1 or 2 miles west 

 from this lake the Pembina Valley is much encumbered Avith bowlders, 

 which in some places are accumulated upon small morainic ridges and 

 knolls. 



The largest bowlder observed within the area of Lake Agassiz south 

 of the international boundary has given name to White Rock station, in the 

 northeast corner of South Dakota, 11 miles north of Lake Traverse. This 

 bowlder, lying 50 feet west of the railway, at a distance of about 25 rods 

 north of the station, measures 18 by 12 feet, with a height of 5^ feet. It 

 is a medium-grained, massive, flesh-colored granite, weathering to a whitish 

 gray. 



Another bowlder of nearh' equal size lies about 50 rods west of the 

 Herman beach, in or near section 12, township 140, range 46, Minnesota, 

 some 6 miles north of Muskoda. Its dimensions are 15 by 12 by 5 feet, 

 and its top is 1,095 feet above the sea. It is gneiss, minutely porphyritic, 

 with white feldspar crystals up to an eighth or a quarter of an inch long. 



A somewhat larger block, exceeding any other noted during my survey 

 of Lake Agassiz and the adjoining region, lies in the northwest quarter 

 of section 9, township 1, range 4 east, Manitoba, on the low ridge 10 miles 

 east of Emerson. It is dark-gray granitoid gneiss, 22 feet long, 8 to 14 

 feet wide, and projecting 2 to 5 feet above the surface. Among the other 

 plentiful bowlders of that vicinity none was seen exceeding 7 or 8 feet in 

 dimensions. Like many of the smaller bowlders throughout this prairie 

 region, this block is surrounded by a slight depression 1 to 3 feet below 

 the adjoining ground; and a careful examination sliows that some of its 

 projecting corners and edges are smoothly jxilished. These dej)ressions 



