THE PELISTOCENE OR GLACIAL PERIOD 857 



locality, and tolerably constant in direction over considerable areas. 

 When large areas are considered, the striae are sometimes far from 

 parallel; but their. departure from parallelism is generally according 

 to a definite system (Fig. 571). The direction of striae corresponds 

 with the- direction in which the drift was transported. 



Besides the striae, grooves, etc., on the bed rock, there are often 

 other details of surface which are equally characteristic. Minute 

 protuberances of surface often show more wear on one side than 



Fig. 570. Terminal moraine topography near Oconomowoc, Wis. (Wis. 



Geol. Surv.) 



on the other (Fig. 572), and minute depressions (Fig. 573) show 

 analogous features. 



9. The shapes of rock hills. The rock knolls which were left 

 bare when the ice retreated often show peculiarities of form and 

 surface which are distinctive. Like the minute protuberances of 

 surface just referred to, rock hills over which the ice passed were 

 worn more on the side from which the ice approached (the stoss 

 side) than on the other (Fig. 211, p. 257). Bosses of rock which 

 do not show notably unequal wear often show distinct smoothing. 

 Projecting glaciated knolls of rock which show the characters seen 

 in Fig. 225, p. 269 are known as roches moutonnees. A succession 

 of roches moutonnees generally gives fairly accurate information 



