PRE-CAM BRIAN ROCKS OF NEWFOUNDLAND 457 



In view of the unknown age of this formation, and because of its 

 characteristic development and typical outcrops in the vicinity of 

 Avondale, Conception Bay, the writer proposes the name Avondale 

 volcanics to designate this series, which comprises rocks of direct 

 volcanic origin, together with a small amount of interbedded more 

 or less waterworn volcanic materials. They constitute a formation 

 of wide geographical extent — 200 miles along the strike and 100 

 miles or more across the strike — and of great but unknown thick- 

 ness, at least several thousand feet, forming so far as is known the 

 basal member of the later pre-Cambrian or Avalonian system of 

 Newfoundland. Interbedded rhyoUte and plagioclase basalt flows, 

 with corresponding breccias, crystal, lithic, and vitric tuffs, volcanic 

 dust beds, and average tuffs, together with volcanic conglomerates, 

 sandstones, and slates are comprised within the series. 



The beds are in a highly disturbed condition, with a prevailing 

 steep dip, and are affected by intense and often profound faulting. 

 They are exposed on the cores of major anticlines or are brought to 

 the surface on the upthrow sides of great faults. The degree of 

 metamorphism which the rocks have suffered is in general moderate, 

 though locally intense, and is manifest for the larger part merely 

 in the development of a slaty cleavage. Secondary minerals, except 

 those of surface origin, are confined almost exclusively to sericite 

 and quartz in the acid rocks and chlorite with sericite, epidote, and 

 calcite in the basic rocks. Along certain shear zones in the acid 

 rocks pyrophyllite, quartz-pyrophylUte, and pinite schists have 

 formed through replacement, while in certain basic rocks copper 

 ores have been deposited along close-set narrow fractures and in 

 vesicles of the flows. Ore in quantities of commercial importance, 

 however, has not yet been found. 



In view of the great age of the rocks the lack of intense meta- 

 morphism and the frequent preservation of delicate primary 

 structures are striking. Indeed there is little doubt that, with 

 search, practically every structure and texture found in the Tertiary 

 and recent volcanics might also be found in these ancient pre- 

 Cambrian volcanics. 



One of the most interesting discoveries in this series was the 

 presence of volcanic necks intruded through the breccias and tuffs. 



