THE 



JOURNAL OF GEOLOGY 



^ MAY-JUNE, 1893. 



ON THE TYPICAL LAURENTIAN AREA 

 OF CANADA. 



The name Laurentian was given by Logan in 1854 to the 

 great series of rocks forming the Laurentides or Laurentian 

 Mountains, a district of mountainous country rising to the north 

 of the River and Gulf of St. Lawrence, and extending in an 

 unbroken stretch along the shore of the latter from Quebec to 

 Labrador, a distance of nine hundred miles. This district, with 

 its continuation to the west as far as Lake Huron, being situated 

 in the Province of Quebec and the adjacent portion of the Prov- 

 ince of Ontario, and forming part of the main Protaxis of the 

 continent, is the "Original Laurentian Area" of Logan. The 

 Laurentian rocks are now known to extend far beyond the limits 

 of this area to the west and north, constituting, as they do, by 

 far the greater part of the Protaxis, and underlying (with subor- 

 dinate patches of Huronian) an area of somewhat over two million 

 square miles. ^ The area above referred to is, however, the one 

 which was first studied and described; it is the "Typical Lauren- 

 tian area," and to it the observations in the present paper will be 

 as far as possible confined. 



A general exploration of the area in question, and a more 

 detailed study of a small part of it^ — the Grenville District — 

 situated in the counties of Argenteuil and Terrebonne in the Prov- 



' Accepting the distribution of the Laurentian in the far north, given by Dr. G. M 

 Dawson, as correct, the area is 2,001,250 square miles. This does not include the out- 

 lying and separated areas occurring in Newfoundland, New York State and Michigan. 

 Vol. I.— No. 4. 325 



