292 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Palache and the writer*^ to wliich reference may ])e made for details. 

 These pipes he wholly within the granite, and it is certain that one, and 

 probably two, did not even reach the present eroded surface of the 

 granite. It is thought that they represent relatively siliceous, water- 

 rich segregations formed at greater depths in the magma. 



Vein phenomena. 



Occasional quartz veins occur in the granite and granite-porphyry. 

 They are generally small affairs measuring from ^ to 1 inch in width 

 but have usually a considerable length and appear to reach deep into 

 the rock. Several of these have been referred to by Dale as occurring 

 in some of the quarries. They usually contain small amounts of 

 fluorite and some of them sphalerite, galena and chalcopyrite. Similar 

 sulphides were noted in the pegmatite pipes. 



Dike Phenomena. 



As has been noted earlier in the paper, dike phenomena connected 

 with the intrusion of the alkaline rocks are inconspicuous. With 

 the exception of a few small pegmatitic dikes or streaks and of two 

 narrow and short microgranite dikes cutting the granite, the dike 

 phenomena of the area is confined to the few granite dikes cutting the 

 cover-porphyry in the region about Slide and Scamaug Notches, and 

 to those dikelets or apophyses invading the slates for a short distance 

 from the actual contact. These latter have been described and figured 

 in some detail by Professor Crosby and appear to be merely offshoots 

 from the main mass of granite. They are for the most part small 

 affairs though in a few instances they appear to have attained con- 

 siderable size. Some of the larger ones are of about the same grain 

 as the granite; the smaller ones are quite fine. None of them with 

 the exception of the dikes in the Pine Tree Brook Reservation appear 

 to possess any noteworthy characteristics not fully covered by Crosby's 

 descriptions. 



The last mentioned dikes cut the slate and also the only series of 

 diabase dikes which are known to be older than the alkaline rocks of 

 eastern Massachusetts (see special map Pine Tree Brook Area). The 

 slate cover in this area is very thin, in fact, forms hardly more than 



16 These Proceedings, 47, No. 4 (July, 1911). 



