BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 12, pp. 377-394, PLS. 33-34 SEPTEMBER 4, 1901 



GEOLOGY OF RIGAUD MOUNTAIN, CANADA 



* BY OSMOND EDGAR LE ROY ^ 



{Read before the Society December 28, 1900) 



CONTENTS 



Page 



Introduction 377 



Topography 378 



General geology 381 



Petrography 383 



Hornhlende syenite 383 



Quartz-syenite porphyry 386 



Quartz porphy ry ' 388 



Aplitic dike 389 



Laurentian hornblende-granite gneiss 390 



Amphibolite 390 



Relation of Rigaud to the other igneous hills in the vicinity 390 



Grenville area of syenite and porphyry 391 



Petrography 391 



Hornblende syenite 391 



Quartz-syenite porphyry 392 



Relation of the Rigaud and Grenville areas 393 



Summary and conclusion 393 



Introduction 



Rigaud mountain is situated in the northwestern- part of the county of 

 Vaudreuil, Province of Quebec, Canada, and includes in its area the parish 

 of Saint George and parts of the parishes of Rigaud, Saint Redempteur, 

 and Sainte Marthe. It is the most western of a line of hills of igneous 

 origin, which, in the vicinity of Montreal, forms the principal topo- 

 graphic feature of the eastern part of the Paleozoic plain of central 

 Canada. These hills — locally termed mountains — are at no great dis- 

 tance from the border of the V-shaped Laurentian protaxis, and follow 

 a line of disturbance which is almost at right angles to the trend of the 

 Notre Dame range. In westward succession there are Shefford, Yamaska, 



* Introduced by F. D. Adams. 

 LIV— Bull. Geol, Soc. Am., Vol. 12, 1900 ' (377) 



