472 A. F. BUDDINGTON 



The pebbles of the conglomerates in the vicinity of Signal Hill 

 consist roughly of about three-quarters rhyolite-porphyry and the 

 remainder granophyre, intraformational red shale flakes, and quartz, 

 with occasional pebbles of basalt. The rocks of which these pebbles 

 are formed are very similar to the rocks comprised within the 

 Avondale volcanic series, and it is quite possible that they have been 

 derived from that formation.^ 



In their stratigraphic relations, lithology, and mode of origin the 

 Signal Hill series resemble the Jotnian of Sweden, the Torridonian 

 of Scotland, and the Keweenawan of the "Canadian Shield." In 

 the absence of vulcanism, so far as yet observed, they stand in 

 contrast to the Keweenawan and Jotnian, but resemble the Torri- 

 donian. This is of special interest, since it has been shown by 

 Hayes and van Ingen that this district during the succeeding 

 Cambro-Ordovician period had a history which coincided even in 

 minor detail with that of Wales. 



INTRUSIVE ROCKS 



The later pre-Cambrian rocks, more especially tjie early later 

 pre-Cambrian beds, are intruded by several batholiths and stocks 

 of igneous rock and are very intensively cut by dikes. In general, 

 it may be said that the salic rocks have been intruded as molten 

 masses of batholithic or stock type, with few apophyses or dikes, 

 whereas the older basaltic or gabbroic magmas, to a preponderating 

 extent, have been intruded as dikes. 



The rocks, with the exception of the quartz syenite and granodi- 

 orite, whose position is unknown, are given in the order of their 

 intrusion, beginning with the oldest. Those around Conception 

 Bay comprise hornblende granite gneiss, hornblende gabbro and 

 plagioclase gabbro without oKvine but locally quartz-bearing, basic 

 granodiorite, biotite granite and granophyre, quartz syenite, aplite 

 and granophyre dikes intruding the granite, and younger dikes of 

 rhyoHte porphyry and diabase intruding all the older rocks. Near 



^ Murray describes the pebbles of the conglomerate at Signal Hill as composed 

 "chiefly of white quartz, but with occasional pebbles of brown or red jasper, syenite 

 or gneiss and slate." The writer examined 150 pebbles with the entirely different 

 result given above. 



