452 WARREN AND POWERS DIAMOND HILL-CUMBERLAND DISTRICT 



may be connected in origin with the alteration of the magnesium-rich 

 cumberlandite only a short distance away. 



Labradonte porphyry dikes. — Three dikes of labradorite porphyry have 

 been found, all of which cut the Ashton schists. One of them is half a 

 mile east of Sneech Pond, a few hundred feet south of the upper road. 

 A second is found north of Iron Mine Hill outcropping in a north-south 

 road. A third and narrow dike (4 inches) is noted by Johnson,^^ cut- 

 ting the gabbro southwest of Iron Mine Hill. 



At the first locality the rock is dark gray and badly weathered, and the 

 large labradorite phenocryst&, many of which were one inch long, have 

 now in large part disappeared, calcite being deposited in their place. A 

 thin-section shows that the rock consists of large labradorite phenocr\sts 

 in a fine groundmass of lath-shaped labradorite, biotite, calcite, magne- 

 tite, and quartz. 



In the dike north of Iron Mine Hill the rock is also dark gray in 

 c-olor, but is fine grained. The feldspars are about one-eighth of an inch 

 long, and are well striated. There are several outcrops in this locality, 

 but the contact with the Ashton schist is not exposed. The dike is cut 

 by numerous stringers of Milford granite. 



The dike east of Sneech Pond shows shearing and long weathering. 

 The age of these dikes is ]io?t-A>htnn schist, pre-^Iilford granite, proba- 

 bly late pre-Cambrian. 



MIDDLE DEVOXIAX 



Quartz diorite. — Quartz diorite outcrops in four localities in the area 

 mapped. The largest and most conspicuous is a mass of irregular out- 

 line beginning west of West Wrentham and extending south and south- 

 west toward Iron Mine Hill. The boundaries of this mass are concealed 

 by drift. Another mass is found south of Grants Mills. It outcrops in 

 several places and appears to underlie the valley at this place. A third 

 locality is found at the extreme southern end of the area, south of Hunt- 

 ing Hill. Here again lowlands and drift conceal most of the bedrock. 

 The fourth localitv is a dikelike mass only a few square feet in area, so 

 far as can be judged from the outcrop, a half-mile north of Albion. 

 Emerson and Perry mapped this outcrop and reported another "at the 

 northern foot of Copper "Mine Hill, on the northern border of the green 

 schist area at the contact of the schist and the granite." ^' This outcrop 

 was not found by the writers, and is therefore not mapped. 



The main mass of quartz diorite is well exposod both west and soutli- 



» Loc cit. 

 »0p. cIt. p. 45. 



