GENERAL GEOLOGY 499 



Altered volcanics of both acid and basic types are the oldest, while 

 closely associated with them are large areas of stratified rock which are 

 thought to be in part at least much altered tuffs. Serpentines occur 

 among the earliest sediments and probably also cut others of somewhat 

 later age. The diabases and later gabbro-diorites, which are closely asso- 

 ciated with the serpentines in position, as well as the granites, which lie 

 to the southeast of the Appalachian ridges, and the syenitic rocks of the 

 Monteregian hills to the northwest, are later in age than any of the sedi- 

 ments. Still later than these are the dikes of camptonite, diabase, and 

 bostonite which cut any of the rocks already mentioned and are them- 

 selves little altered in character or disturbed in position. 



Extreme metamorphism has obscured or totally obliterated much of the 

 fossil evidence which the sedimentary rocks might otherwise have fur- 

 nished, while such fossil evidence as remains is rendered less useful for 

 precise correlation by the peculiar conditions under which these sediments 

 have probably been deposited. They have accordingly been designated 

 in geological nomenclature as the Quebec group.* The group of rocks 

 thus named by Logan and Billings was considered by them to be equiva- 

 lent to the calciferous and chazy formations in part. Subsequently, 

 however, Selwyn and Ells distinguished within the area assigned to the 

 Quebec group the measures now mapped as pre- Cambrian, showed much 

 of the supposed Silurian to be Cambro-Silurian, and classed the greater 

 part of the remaining rocks as Cambrian. 



The pre-Cambrian comprises three main ridges, which are the prin- 

 cipal physiographic features - of the eastern townships, namely, Sutton 

 mountain, Stoke mountain, and the Boundary Line hills. These ridges, 

 which are roughly parallel, run in a northeasterly course, as determined 

 by the Appalachian folding, and are themselves about 25 miles apart 

 between the Saint Francis and the Chaudiere rivers. 



Previous geological Eesearch 



The rocks composing the ridges just referred to were named argillites, 

 sandstones, chloritic and nacreous schists, and slates, in the first investiga- 

 tions of the Geological Survey under Sir W. E. Logan and Dr T. S. 

 Hunt. In stratigraphical arrangement these ridges were supposed to be 

 synclinal troughs which had resisted denudation better than the interven- 

 ing strata. 



This view was first questioned by Hunt on stratigraphic grounds, and 

 later by Selwyn, both on stratigraphic and lithologic evidence. Doctor 



* Sir W. E. Logan : Geology of Canada, 1863 and later. 



