20G 



cono-lomcnite series, to draw the line between slate and sand- 



CI 



stone, and part of what has been niap[)ed as slate might be 

 otherwise classified. The great elate series above the qonglom- 

 erate consists throughout of a homogeneous gray slate, a hard, 

 firm, but not strictly impalpable rock. It is distinctly siliceous 

 in composition, and a fine granular structure is often apparent 

 under a lens. Although usually more or less distinctly banded, 

 the stratification being marked by laminae of alternating colors, 

 the Hingham slates, whether in the conglomerate scries or in 

 the slate series, are rarely shaly or exhibit a lamination cleavage ; 

 and only to a limited extent, as in the vicinity of Pluit's Cove, 

 is the true slaty cleavage, transverse to the bedding, well 

 developed. A very perfect cuboidal or rhomboidal joint- 

 structure can be seen in many exposures. 



DETAILED STRUCTURE OF NORTHERN HINfJHAM. 



We are now ready for a systematic, ledgc-to-ledge study of 

 the bedded rocks of Hingham, following, as at Nantasket, the 

 topographic order of the outcrops. The village area, bordering 

 the railroad, south of the granite axis, is in most respects a 

 convenient and natural starting point for a detailed examina- 

 tion of the sedimentary and volcanic rocks. The section 

 between Beal Street and Real's Cove is more complete, and 

 presents a normal rather than an inverted succession of the 

 strata, but the ledges are less continuous, and the beds are 

 much less easily traced along the strike. Moreover, it is a 

 woode<l and swampy tract, while the village area is elevated 

 and open, and readily accessible, in spite of the numerous 

 houses and fences. 



T/ie Village Area. 



This is the area represented on the first of the special 

 maps (PI. 7), embracing all the ledges between Main Street 



