

OF CENTRAL CANADA PART III. 181 



hand, syenite is represented in the Metamorphic Series by syenitic 

 gneiss, and to some extent by amphibolite or hornblende-rock. 

 Syenite, as already explained, is very frequently porphyritic red or 

 occasionally white crystals of feldspar appearing on a dark or black 

 groun 1, or green or black crystals of hornblende being imbedded in 

 a reddish granular mixture of the usual components. 



In Canada, eruptive syenites appear to be confined mostly to 

 Laurentian areas. The most remarkable example is the great 

 syenitic mass described by Sir William Logan as covering a space of 

 about thirty-six square miles in the Townships of Grenville, Chatham, 

 and Weritworth, near the left bank of the Ottawa. It consists chiefly 

 of red and white orthoclase, with black hornblende and a little 

 quartz ; mica being also present in one portion of the mass, which 

 thus shows a transition into syenitic granite. Dykes pass from the 

 main body of the syenite into the surrounding beds of crystalline 

 limestone and gneiss. Two other series of dykes or eruptive masses 

 occur in connection with the syenite of this locality. Some of these 

 masses, consisting of a compact base of petro-silex, or intimate mix- 

 ture of quartz and feldspar, with imbedded crystals of red orthoclase 

 and fragments of gneiss and other rocks, traverse the syenite, and 

 hence are of newer origin ; whilst others, consisting of trap or green- 

 stone, are cut off, or interrupted in their course, by the syenite, and 

 are therefore of anterior date. Dykes of syenite also occur, here and 

 there, throughout the Laurentian country between the Ottawa and 

 Lake Superior. 



Anorthosites : The term " anorthosite " was first applied by Dr. 

 Sterry Hunt to a rock-mixture of various anorthic or triclinic feld- 

 spars, at that time regarded as a stratified crystalline formation or 

 rock of the metamorphic series proper. Feldspathic rocks of this 

 character occur in the counties of Argenteuil, Terrebonne and Mont- 

 morency, in the Province of Quebec, where they were thought to 

 represent the so-called Upper Laurentian, Labrador or Norian for- 

 mation, but they are now regarded by Dr. A. C. Selwyn, the present 

 director of the Geological Survey of Canada, as eruptive products of 

 Laurentian age, and this opinion, although not absolutely free from 

 doubt, is probably tne correct view. As stated in the previous 

 edition of this work, their supposed stratification is exceedingly 



