Some Dykes cutting Laurentian Series. 



485. 



proportion of these minerals forms an intergrowth of 

 micropegmatite. The most important accessory minerals 

 are magnetite and apatite. The latter occurs in needle- 

 like forms, and, curiously enough, is most abundant in the 

 minerals filling the interstitial spaces. The rock at the- 

 contact, and in the centre of the wider parts of the dyke, 

 is seen to vary considerably, specimens from the centre 

 being somewhat coarser grained and more acid. The 

 latter point is illustrated by the more abundant occur- 

 rence of quartz and hornblende, and by the shorter and 

 broader form of the feldspar, which commonly shows 

 twinning according to both the albite and pericline laws.. 

 Phenocrysts of plagioclase of the first generation are also- 

 less abundant near the centre of the dyke. A specimen 

 of the rock, taken some distance from the contact, was 

 found to contain 52*96 per cent, of silica. Thin sections 

 of the rock taken from a number of dykes in the town- 

 ship of Bedford were found to be similar in character to 

 those taken from the North Burgess dykes. These rocks,, 

 from both townships, appear to belong to the gabbro 

 family, the more acid representatives of which frequently 

 contain 53 per cent, of silica. We believe that they 

 should be described as quartziferous gabbro porphyrites. 

 The following table will show the relation they hold to> 

 other gabbro and diorite dyke rocks which have been, 

 described from other countries : — 



Dyke Rocks 



Gabbro. 

 Gabbro aplite. 

 (Beerbachite). 1 



Gabbro porphyrite. 



( ) 



Gabbro lamprophyre. 

 (Odinite) 1 



Diorite. 

 Diorite aplite. 



(Malchite). 2 



Diorite porphyrite. 

 (Orbite). 1 



Diorite lamprophyre. 

 (1. Kersantite). 

 (2. Camptonite).. 



1 Dr. C Chelius : Notizbl. Ver. Erdk. Darmstadt, IV., Folge, 1891 u. 1892. 



2 Prof. A. Ossan : Mitth. grossli. bad. Geol., Landesanst, II.. 380. 



