164 RALPH S. TARR 



ably straight, smooth sides, the steepened slope, and the hanging 

 valleys whose characteristics suggest ice-erosion origin. 



CAPE ANN, MASSACHUSETTS 



This cape, extending into the sea north of Boston, has upon it an 

 interesting morainic deposit in which there are large numbers of 

 bowlders (Fig. 2), in some cases with bands of bowlders piled one on 

 the other, making bear-den moraines (Fig. 6). It is no overestimate 

 to state that there are tens of thousands of bowlders on the Cape, and 

 that fully 90 per cent, of these are of local origin, especially granite 



Fig. 2. — Bowlders in the Cape Ann (Mass.) moraine, showing the ordinary con- 

 dition of the moraine surface. 



of which the Cape is chiefly made. So far no satisfactory explanation 

 of this marked accumulation of local bowlders has been proposed. 

 Years ago I did work on the geology of Cape Ann as an assist- 

 ant to Professor Shaler, and the result of his studies was published 

 by the U. S. Geological Survey. 1 Numerous visits since then, 

 together with the fact that quarrying operations have opened up 

 scores of new exposures, have furnished new facts which show con- 

 clusively that ice-erosion on Cape Ann was very ineffective, and 

 that the large numbers of bowlders are probably directly due to this 

 fact. Indeed, they evidently represent the slightly moved bowlders 

 of decay prepared for removal before the last ice-advance. The evi- 

 dence of moderate ice-erosion is of several kinds, as follows. 



1 Ninth Annual Report, U. S. Geological Survey (1887-88), pp. 529-611. 



