_PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 83 
Dale? traced the boundary of the pre-Cambrian and the Cam- 
brian rocks of Vermont for a distance of 60 miles and finds them to 
be structurally discordant and unconformable. The pre-Cambrian 
rocks include various granite gneisses, aplite gneiss, metamorphic 
arkoses, quartzite, conglomerate with pebbles of quartzite, albitic 
sericitic schists, and graphitic sericitic schist. 
Eaton? states that the pre-Cambrian rocks of South Mountain, 
Pennsylvania, near 40° 20’ north latitude and meridian 76° 10’ 
west longitude, consist mainly of granite, diorite and gabbro 
gneisses cut by granite pegmatites. These gneisses probably cor- 
respond in age and composition to the Losee, Byram, and Pochuck 
gneisses of eastern Pennsylvania and New Jersey. 
Emerson? recognizes two belts of pre-Cambrian rocks in Massa- 
chusetts, a western belt forming the backbone of the Green. 
Mountains, the eastern belt extending from Rhode Island through 
- Worcester and Essex counties, Massachusetts. The oldest 
rock in the western belt is the Hinsdale gneiss, a coarse granitoid 
gneiss including beds of limestone, quartzite, micaceous graphitic 
schists. Coarse feldspathic rocks locally replace the limestones. 
Hornblendic and fibrolitic rocks are also included in the Hinsdale 
gneiss. In the upper portion of the Hinsdale gneiss is the Cole 
Brook limestone, a coarse magnesian limestone, highly meta- 
morphosed and about 600 feet thick. A more quartzose gneiss 
than the Hinsdale is called the Washington gneiss. The dominantly 
igneous pre-Cambrian rocks of western Massachusetts include the 
Stanford granite gneiss, titanite-diopside, diorite aplite, Lee quartz 
diorite, Becket granite gneiss, and dunite. 
The oldest pre-Cambrian rocks in the eastern belt is the North- 
bridge granite gneiss. With apparent unconformity, it is overlain 
successively by the Westboro quartzite and the Marlboro formation, 
both doubtfully pre-Cambrian. The latter is a biotite schist. 
tT. Nelson Dale, “‘The Algonkian-Cambrian Boundary East of the Green Moun- 
tain Axis in Vermont,” Am. Jour. Sci., 4th Ser., Vol. XLII (1916), pp. 120-24, 1 fig. 
2H. N. Eaton, “The Geology of South Mountain at the Junction of Berks, 
Lebanon, and Lancaster Counties, Pennsylvania,” Jour. Geol., Vol. XX (May-June, 
1912), Pp. 331-43, 2 figs. 
3B. K. Emerson, “Geology of Massachusetts and Rhode Island,” U.S. Geol. 
Surv., Bull. 597 (1917), 289 pp., 10 pls., 2 figs. 
