STRUCTURAL FEATURES OF THE PRE-CAMBRIAN 199 



Pontiac area. — The Pontiac area (Fig. 12) lies far to the south 

 of the Brock, Broadback, and Mattagami areas but its rocks are 

 strikingly similar. It is found to the south of the National Trans- 

 continental Railway with its western end close to the Ontario- 

 Quebec boundary; it is nearly one hundred miles in length by 

 twelve in breadth. The rocks have been studied by M. E. Wilson^ 

 and J. A. Bancroft.^ The following is a summarized account of 

 their descriptions. 



Fig. 12. — The Pontiac area 



The rocks of the region fall into two general classes, a volcanic 

 complex and a series of metamorphosed clastic sediments, termed 

 by Wilson the Pontiac series. The Pontiac series is cut off on the 

 south by intrusions of granite; the volcanic complex lies to the 

 north of it. The band of sediments averages ten miles in width; 

 the major part of this, about nine miles, is underlain by mica schist, 

 with which is associated some hornblende schist and amphibolite. 



^ Geol. Surv. Can., Mem. No. 39, 1914. 



^Report on Mining Operations for iQii, Department of Colonization, MineS; and 

 Fisheries, Quebec, p. 160; 191 2, p. 199. 



