PRE-CAMBRIAN ROCKS OF NEWFOUNDLAND 475 



The colorless augite is almost completely altered to pleochroic green 

 hornblende and chlorite. A chemical analysis of this rock is given 

 on page 476, No. 3. 



Outcrops of a quartz syenite are found along the shore to the 

 north of Chapel Cove. This rock has a very limited distribution, 

 occurring in fault blocks brought into their present position by 

 thrusting, and in places the rock is much crushed by the stresses 

 to which it has been subjected. In the hand specimen the rock 

 appears to be a white, medium-grained syenite, consisting of an 

 aggregate of feldspars averaging 5 mm. in length. In thin section 

 the rock is seen to consist of an aggregate of plagioclase feldspars, 

 predominantly albite and to a minor extent oligoclase, with a 

 groundmass of quartz and orthoclase in micrographic intergrowth 

 filling the interstices. The rock is crushed and exhibits cataclastic 

 texture in a high degree. A chemical analysis of this rock will be 

 found on page 476, No. 4. 



The backbone of the St. John's Peninsula is mapped by Howley 

 (1907) as Laurentian. This rock in its northern half was found by 

 the writer to bear intrusive relations to the Avondale volcanics and 

 to constitute a granite batholith five to six miles in width and about 

 forty miles in length, if its boundary to the south continues to 

 coincide with that of Howley's Laurentian area. The eastern 

 boundary, where it was followed by the writer for several miles, is 

 deHmited by a fault plane. Along the west side the beds are very 

 much disturbed and folded. The rock is a pink, medium-grained, 

 equigranular, biotite granite, consisting essentially of quartz, 

 orthoclase, albite, oligoclase, and chlorite, the latter believed to be 

 derived from biotite. Fresh flakes of original biotite, however, are 

 found only in occasional sections. A chemical analysis of the rock 

 appears on page 476, No. 5. 



One of the most striking and interesting features of the geology 

 along Smith and Random sounds at the head of Trinity Bay is the 

 way in which the early green slates of that region have been rent, 

 riven, and intruded by a great series of approximately parallel dikes 

 of porphyrite and basalt. At one locality there were counted 32 

 dikes in a distance of about 350 yards. As a rule, however, the 

 dikes are not as frequent as this ; yet they are never absent for any 



