267 ■ 



Nantasket, Weymouth, Brighton, and Nahant, — is it possible 

 to trace any lithological resemblance between these and any 

 crystalline rocks ; and in all such instances the fact, cause, and 

 local nature of the alteration are clear beyond dispute ; and, 

 furthermore, the altered rocks bear no likeness to any known 

 crystallines in this region, save where the conglomerate resem- 

 bles uncrystalline ( ! ) portions of the Sha.wmut breccia, or 

 the sandstone has the hardness of quartzite (and induration is 

 the simplest species of alteration) , or slate and -sandstone have 

 the texture of amygdaloid. In this last case, however, there 

 really is no resemblance, except, perhaps, with a small mass of 

 sandstone at Nantasket ; for the very large amygdules in the 

 slate at Mill Cove, in Weymouth, and East Point, Nahant, are 

 entirely unlike anything observed in the true amygdaloid of the 

 Boston basin. With the exception of the orthoclase crystals in 

 the sandrock of Marblehead Neck, crystalline characters are 

 almost entirely wanting in the Primordial formation. 



Basin of the River Parher. 



The uncrystallines of this contracted basin are of limited ex- 

 tent, and comparatively little importance ; and a few lines will 

 suffice for their description. The only evidences of the Primor- 

 dial age of these sediments are those afforded by (1) their 

 relations to the crystallines, which are, in every essential re- 

 spect, the same as in the Boston basin ; and (2) their litho- 

 logical resemblance to the Boston deposits, a resemblance that is 

 conspicuous only in the case of the pinite conglomerate, and the 

 red beds to be noticed presently. The conglomerate, with pinite 

 pebbles, which is abundant on Kent's Island, is fine-grained and 

 schistose, and indistinguishable from that between the Neponset 

 River and Pine Tree Brook, in Milton, or in the vicinity of 

 South Natick. At all points in the basin of the River Parker, 

 the uncrystallines have an E.— W., varying to E.N.E., stril^e, 

 and a high dip to the north ; agreeing in these respects with the 

 petrosilex and amygdaloid, and appearing to form, with them, 



