210 PROCEEDINGS OF THE AMERICAN ACADEMY. 



and fine-granite would hardly cover over one-half of the batholith as 

 at present exposed. The granite occupies a belt stretching across 

 southern Milton on the north of the Blue Hills, comprises most of 

 the rocks in Quincy and West Quincy, but is replaced by the fine- 

 granite facies in eastern and southern Quincy and part of northern 

 Weymouth. In fact the coarse-granite can hardly be said to occur 

 in the Blue Hills proper except at one point (near Rattlesnake Hills), 

 and in the form of dikes, cutting the porphyry cover, in the region 

 just east of Chickatawbut Hill. As a matter of fact, its southern 

 projections at Rattlesnake Hill and on Pine Hill, in both of which 

 places it comes in contact with the porphyry, show a distinct tendency 

 toward a porphyritic texture thus grading toward the porphyry. 



Crosby states ^^ that normal granite is transitional into "quartz 

 porphyry and fine-granite" in the vicinity of Slide Notch. The writer 

 has examined this section with extreme care and while unable to find 

 any strictly normal granite having certainly the relations ascribed to 

 it by Crosby, has found several well marked, granite dikes essentially 

 of the Quincy type. One of these was first encountered about 75 ft. 

 south of the extreme top of Chickatawbut Hill. It is here about 

 20 ft. wide, apparently nearly vertical in dip, and strikes about S. (lO E. 

 and reaches a width of certainly 30 ft. It has been traced across the 

 eastern member of Chickatawbut as far as the steep slopes of Slide 

 Notch near its lower end. A second dike, nearly 50 ft. wide at one 

 point, haA'ing aliout the same dip and strike as the first, outcrops at 

 the entrance of the Notch. It has been traced for at least 400 ft. 

 On the western side of the Notch, it seems to flatten in dip and there 

 is also a smaller dike, probably an offshoot of the main one, a few feet 

 to the south. It is to be noted that these dikes show in places along 

 their contact with the granite-porphyry a slight development of very 

 fine graphic-granite, and that they also contain numerous inclusions 

 or segregations of dark porphyry and fine-granite exactly similar to 

 those found in the main granite. Again near the head of Scamaug 

 Notch, relatively coarse granite outcrops in the form of two dikes. 

 While it is clear that at least part of the granite exposed at this point 

 is a dike intrusion, another part of the granite here does not exhibit 

 clearly marked contacts and is probably, as beheved by Professor 

 Crosby, an exposure of the underlying granite. The character of 

 the granite-porphyry which seems to grade into the granite in one of 

 its outcrops supports this view. 



11 Op. cit., p. 366. 



