194 



streets as far as the Cohasset boundary, tlic ordinary coarse 

 granite can, in spite of the lichens, he seen to form irreguhir 

 dikes in, or to enclose angular fragments and masses of, the 

 diorite. The greenish gray quartz-[)orphyry obsctu-ely exposed 

 in South Street, east of Ifersey Street, in Hingham Village, is 

 probably a dike in the granite , but considerable digging would 

 be required to prove it. In the rear of the first house on 

 Lincoln Street and Fountain Square, north of the Unitarian 

 Church, is a mass, clearly eruptive through the coarse granite, 

 of a compact, flinty, pur[)lish felsite, which has been proved by 

 analysis to agree with the granite in composition. 



The felsite of Hingham is not wholly intrusive, or in the 

 form of dikes. The gray felsite, on the north side of Beal 

 Street, at the western end of the granite, is quite probably 

 part of a surface flow ; and the beautiful red felsite occurring 

 so plentifully in the form of bowlders in the vicinity of Lincoln 

 and TMiaxtcr Streets is unquestionably effusive. The former 

 varies from a slightly greenish gray or white to a pinkisii tint, 

 and encloses many more or less distinct fragments of similar 

 or darker felsite and an occasional fragment of granite. The 

 breccia structure thus resulting is so marked in a portion of 

 the rock that it was at first mistaken for conglomerate ; and 

 the isolated elliptical area on this part of the map marked and 

 colored as conglomerate is really felsite. The exposures of 

 the felsite are not sufficient to show clearly its relations to 

 either the granite, which it seems to overlie, or the melaphyr, 

 which probably once covered it. 



The red felsite of Thaxter and Lincoln Streets is by far the 

 most attractive of all the older rocks of Hingham. Li fact, 

 it is the most beautiful variety of felsite in eastern Massa- 

 chusetts ; and it is also unique in being the only felsite in 

 the entire south shore district which is certainly effusive. 

 Unfortunately, it occurs in an area which is covered almost 

 contimu)Usly by salt marshes and drumlins, and there is prac- 

 tically no opportunity to study it in siln. This rock, which 



