GLACIAL FEATURES OF ST. CROIX DALLES REGION 249 



the modified drift (red outwash) and the gray above, as found in 

 several places in Chisago County. This would indicate a consid- 

 erable interval between the two ice-sheets. 



The story 0} the rocks. — The hard ledges of Keweenawan trap-rock 

 in the Dalles region exhibit good stoss sides, which furnish strong 

 evidence of the direction of ice movement. East of the river, and 

 especially east of the gray terminal moraine, the planed sides are 

 almost invariably the west or northwest slopes of the ledges, the few 

 exceptions being clearly local accidents. These may be called the 

 red stoss sides ; they occur also on the west side of the river, but here 

 the complication of the Kewatin ice is added. Knobs and tails 

 produced from the resisting amygdules in the diabase agree with the 

 story of the stoss sides. Striae have not been well preserved on these 

 rocks, which in general have weathered sufficiently to destroy the 

 scratches. By looking over a large number of ledges, however, 

 plenty of records can be obtained. The location, direction, and 

 significance of these can best be understood from the striae map. 

 While there is considerable variation, owing to the fact that they 

 were made at no great distance from the fluctuating edge of the ice, 

 they tell a consistent tale. The striae are in three sets. 



1. The earliest set of scratches discovered affect only a few out- 

 crops above the bend in the river, four and a half miles due north of 

 Taylor's Falls. In a gully whose stream has cut deeply into the 

 drift and laid bare the Keweenawan, striae reading S. n° E. 1 and 

 S. 1 3 E. were found, accompanied by a more marked set running 

 S. 40 E. Half a mile northeast, the hillside ledges bear striae S. 8° E., 

 S. ii° E., and S. 15 E. As shown on the map, these were probably 

 made when the ice covered the entire quadrangle and was making 

 its terminal moraine at a considerable distance away. The set of 

 striae next to be described, S. 40 E., are better represented on these 

 rocks, but those of the latest, or third, group are absent; suggesting 

 that the ledges became covered by drift and were protected during 

 the St. Croix terminal stage. This protection may explain the pres- 

 ence of the old striae which are not found in less favored places. The 

 weak ice of the gray drift, however, has left a still later set of marks 



1 The directions of striae are all corrected for magnetic variation. 



