WARREN. — ALKALI-GRANITES AND PORPHYRIES. 265 



of the rhombenporphyry, together with inclusions of a somewhat dif- 

 ferent type, are found in the granite on a scale seen no where else in 

 the field. Judging from the character of the granite along this line 

 and its known relation to the contact porphyry, these inclusions can- 

 not lie more than a few yards, and probably feet, below an original 

 slate contact. 



Another prominent exposure of the porphyry is found just north 

 of the Great Dome, particularly beside the Sawcut Notch road which 

 passes by this hill on the north. Small dikelets of the porphyry are 

 to be seen cutting the slate and a considerable exposure of the main 

 mass of the rock at this point is also seen in chilled contact with the 

 slate. A little farther west within the Pine Tree Brook Reser^•ation 

 (see special map) proper, on the Little Dome and about Pine Rock 

 are numerous and excellent exposures although the rock is very deeply 

 weathered in all of them. Several small inclusions of the slate are to 

 be seen in the rhomljen-porphyry and a thin veneer of slate may be 

 found on several ledges, thus confirming the intimate relation of the 

 rock with the slate contacts as shown elsewhere. A little further 

 west and north, in the lots just outside of the reservation at near the 

 point where the Sawcut Notch road enters it, abundant patches of 

 the dark colored porphyry are found included in the large granite 

 dike which here cuts across the slates (see special map). 



Megascopic Characters. — As regards the relative proportions of 

 phenocrysts and groundmass, this porphyry varies widely. From 

 a rock consisting of a black to dark greenish-black, finely granular 

 groundmass, holding a few white or greyish white to nearly transparent 

 phenocrysts of unstriated feldspar, it varies through more profusely 

 porphyritic phases to those in which the groundmass is practically 

 indistinguishable to the eye, and indeed even under the microscope 

 is so small that the rock is practically a syenite. This later extreme 

 phase, it may be noted, has been found in only one or two good sized 

 ledges in the Pine Tree Brook area. The general run of the porphyry 

 may be descriljed as dopatic to sempatic, viz. groundmass dominant 

 or equal to the phenocrysts in amount. 



The feldspar phenocrysts are as a rule somewhat longer than broad 

 and in their longest dimension will range from perhaps 2 mm. to nearly 

 a centimeter. The most characteristic thing about them is the gently 

 curved sides and the acute terminations of a large proportion of them. 

 The habit is quite strongly "rhomben." A considerable number of 

 them are not simple crystals but consist of two or more parts. It 

 may often be noticed that these parts terminate in two or more 



