215 



projecting through a thin and approximately horizontal bed of 

 conglomerate ; although the surfiice relations of the two rocks 

 might be partly explained by faulting. That the granite is not 

 younger than and eruptive through the conglomerate is proved 

 beyond the shadow of a doubt by tlie nature of the contact and 

 the composition of the conglomerate. The latter is made up 

 very largely, especially where it lies directly upon or against 

 the granite, of the angular and half rounded debris of exactly 

 the same coarsely crystalline red granite ; and the fragments, 

 wliich range from single grains of quartz and feldspar to 

 masses two feet or more in diameter, are sometimes only injper- 

 fectly separated from the parent ledge, the finer sediment 

 appearing to penetrate cracks in the granite. The relations are 

 essentially the same as on Rocky Neck and Granite Plateau of 

 the Nantasket area, where the basal conglomerate rests upon 

 the granite ; and they also agree with the contacts resulting 

 from the rapid deposition of coai-se sediments over a disinte- 

 grated land-surface, as recently described by Professor 

 Pumpelly^ and Professor Emerson.^ On purely structural 

 grounds, this conglomerate should certainly be correlated with 

 the basal conglomerate of Nantasket : which would, apparently, 

 separate it widely from all the other Hingham strata. The 

 melaphyr marked on the map as outcropping in the midst of 

 this basal conglomerate, probably overlies it. It is amygda- 

 loidal and otherwise similar to the rest of the Hingham mela- 

 phyr, but may, of course, be the equivalent of any of the 

 earlier basic flows of Nantasket. 



This completes the detailed examination of the ledges of the 

 Village area. If, as appears necessary, we regard the series 

 as inverted, the general structure and the relations to the 

 granite must be approximately as represented in the section 

 accompanying the map. A long, narrow block of strata is 

 faulted down between walls of granite, the drop on the north 



1 Bull. geol. soc. Anierii-a, vol. 2, p. 209-224. 

 ■^ Bull. geol. soc. America, vol. 2, p. 451-456. 



