476 



A. F. BUDDINGTON 



great distance. Their general strike is approximately north-south. 

 About half the dikes are between two and five feet in width, and 

 the rest are about equally divided between dikes ten to fifteen feet 

 and those thirty or more feet in width. In addition to the dikes 

 in the slate series several dikes and sills were found intruding the 

 Cambro-Ordovician rocks, and dikes in the Signal Hill and Random 

 formations are present but rare. The porphyrite dikes are variable 

 in their mineralogical composition and comprise hornblende por- 

 phyrites, labradorite porphyrites, and augite porphyrites or basalts. 



TABLE V 



Chemical Analyses or Instructive Igneous Rocks around Conception Bay 



SiO.... 

 A1A-- 

 FeA-- 

 FeO... 

 MgO.. 

 CaO... 

 Na.O.. 

 K.O... 

 H.0+. 

 H.O-. 

 TiO.. . 

 MnO.. 



59.18 



18.21 



2-73 

 3.62 



2-51 



23 



3.26 

 1. 8s 



. 20 

 Undet. 



.16 



71.82 



16.07 



1 . 22 



1 .60 



■ 40 



1.66 



3-27 



3-07 



• 71 



.19 



Undet. 



•13 



Total. 



99-77 



99 59 



99-79 



99.66 



100. 14 



1. Hornblende gabbro from about 6 miles south of Manuels. 



2. Quartz bearing gabbro from Holyrood Butterpot. 



3. Granodiorite from near Woodfords. 



4. Quartz syenite from Chapel Cove. 



5. Biotite granite from interior of St. John's Peninsula. 



The former are found in the pre-Cambrian slates, but only the last 

 named in the Cambro-Ordovician beds. 



In the region about Conception Bay the granite of the Holyrood 

 batholith, the gabbro, quartz syenite, and dikes of rhyohte porphyry 

 and diabase are all overlain unconformably by Lower Cambrian 

 sediments. SaUc dikes were not found intruding beds younger than 

 the Conception slate series, and femic dikes are far less frequent in 

 formations above this series than in those below it and constituting 

 it. Whether this is due to the different character of the formations, 

 to their different stratigraphic position, or to their different age, 



