622 THE PLEISTOCENE PERIOD 



sharply defined, and the surface of the rock is likely to be fresh and 

 firm (Fig. 145). This relation is in contrast with that between 

 mantle rock and the underlying formations where there is no drift 

 (Fig. 152). 



8. Striation and planation. 1 The rock surface beneath the 

 drift, and especially beneath the unstratified drift, is in many places 

 polished, planed, striated (Fig. 145), and grooved. These features 

 are widespread throughout the drift-covered area, and they appear 



Fig. 514. Terminal moraine topography near Oconomowoc, Wis. 



at all elevations where there is drift. The striae on the bed rock 

 beneath the drift are generally parallel in any given locality, and 

 tolerably constant in direction over considerable areas; but when 

 large areas are considered, the striae are in some places far from par- 

 allel. Their direction corresponds with the direction in which the 

 drift was transported. 



9. Shapes of rock hills. Many rock knolls which were left 

 bare when the ice retreated show peculiarities of form and surface 

 which are distinctive. They were worn more on the side from which 

 the ice approached (the stoss side) than on the other (Fig. 153). 

 Bosses of rock which do not show notably unequal wear show dis- 

 tinct smoothing. Projecting glaciated knolls of rock which show the 

 characters seen in Fig. 167, p. 162, are known as roches moutonnees. 



1 Seventh Ann. Kept., U. S. Geol. Surv., has a full discussion of this topic. 



