On the Norian or "Upper Zaurentian" Formation. 429 



almost reaches in the region of Franklin's Bay, east of 

 the mouth of the Mackenzie Biver. ^ 



It is not necessary here to discuss at greater length the 

 origin of this great complex of gneisses and other crystal- 

 line rocks which make up the protaxis. Let it suffice 

 to remark that sedimentary deposits doubtless partici- 

 pate in the composition, at least of the Upper Lauren tian 

 (Grenville division) and the Huronian. 



The Appalachian protaxis, especially that part which 

 lies in Canada, has probably been uplifted through more 

 recent foldings, but it had attained the main features of 

 its present form as early as the Cambrian period. It is 

 probable, however, that at that time, just as later, in the 

 Lower Silurian period, a large area in the interior of the 

 chief protaxis around the Hudson Bay was covered by 

 the sea. Bound about this already folded protaxis the 

 sediments were deposited during the Cambrian, Silurian, 

 Devonian and later periods, while the intrusions of anor- 

 thosite took place along the edge of the main protaxis — 

 that is, of the old continent — and formed a belt around 

 the oceanic basin, in which the Cambrian rocks were 

 afterwards deposited. These sediments were, first in 

 LTpper Silurian times but repeatedly during subsequent 

 ages, subjected to great lateral pressure, exerted from the 

 direction of the Atlantic basin. These sedimentary rocks, 

 together with the crystalline rocks of the Apalachian 

 protaxis, were, in this manner thrown up in a series of 

 great folds which form the Apalachian chain. 



These foldings were naturally accompanied by deep- 

 seated alteration and metamorphism, and resulted in the 

 development of a great fault along the west side of the 

 chain, which extends in a southerly direction into the 

 United States. To the west of this fault lie the horizontal 

 and unaltered Cambrian and Silurian strata which form 

 the great plains of Central Canada. 



