1 68 RALPH S. TARR 



That these masses should have resisted ice-erosion is remarkable; 

 and that this erosion has not extended below the level of the dis- 

 integrated granite is clear proof of its general weakness on Cape Ann. 



The till.— One of the most striking features of the till of Cape 

 Ann, aside from its bowldery nature, is its sandy and gravelly con- 

 dition. In some cuts the till very closely resembles the disintegrated 

 gravel above described, and everywhere it seems to contain a large 

 percentage of this decayed material. From the field evidence I 

 am convinced that the till of Cape Ann is in large part made up of 

 gravel disintegrated before the last ice-advance and pushed forward 

 a short distance to its present position. 



The bowlders and bear-den moraines. — It has been stated above 

 that the bowlders of Cape Ann are prevailingly local, probably as 

 much as 90 per cent, being of rocks at present in place on the Cape. 

 Many of these are angular (Fig. 2), with joint-plane faces, as if 

 broken from a ledge and carried a short distance without attrition. 

 On the other hand, many, although carried only a short distance, are 

 well rounded. 



Both of these conditions are readily explained on the theory that 

 they represent the dislodged products of decay prior to the ice- 

 advance. Fragments surrounded by disintegrated gravel were 

 rounded; those broken from the markedly jointed sections had 

 angular faces. No other explanation that has occurred to me will 

 account for this vast number of local bowlders; and the fact that 

 some unremoved masses are left (Fig. 4) points clearly to this 

 explanation as the true one. 



The bear-den moraines (Fig. 6), representing bands of excessive 

 bowlder accumulations, occur at various levels, so that they can 

 scarcely be assigned to marine action, on the assumption that when 

 they were accumulated the sea stood at the ice-front. Opposed to 

 this theory also is the further fact that some of the occurrences are 

 on protected valley slopes where sea-action could not have been very 

 effective. So far as observed, they are all situated on lee slopes, 

 which suggests that they were combed over the edges of the hills by 

 ice-push, and perhaps added to accumulations which, being in the lee, 

 the ice was incapable of removing. The only alternative explanation 

 that appears is that they owe their origin to the action of water run- 



