8 9 



ORDER OF SUCCESSION. 



In proper order of succession, the earliest rocks are 

 exposed on the St. Lawrence river shore in a narrow belt 

 of black Cambrian or Cambro-Ordovician shale to be seen 

 at Cap Rosiers and thence up the river {Rosters 

 shale). Following immediately south (see map for posi- 

 tion and direction of these belts) rise the steep cliffs of 

 Lower Devonian (St. A lb an, Bon Ami and Grande Greve 

 beds). In the ascent from the low wave cut plateau of 

 Cap Rosiers to the heights of the Bon Ami cliffs, 

 one traverses the thrust plane between the Rosiers shale 

 beds and the St. Alban lime shales, along which most of 

 the Ordovician and all the Silurian to an unknown thick- 

 ness has been squeezed out.* 



This is the Forillon fold, the southern flank of the Cap 

 Rosiers overthrust. In it the Devonian St. Alban, 

 Bon Ami and Grande Greve beds, all conformable, are 

 inclined quite uniformly west of south at angles of 25°-30°, 

 but the Cambro-Ordovician Rosiers shales on which they 

 lie are almost vertical and always highly distorted. It is 

 not now possible to estimate the degree of this overthrust 

 or extent of the Devonian cover but it would seem to 

 have at least extended 8 miles (14-4 km.) seaward to the 

 50 fathom line. If the Silurian has actually been squeezed 

 out by the overthrust it is probable that a formation of 

 very great thickness has thus disappeared from the succes- 

 sion, for at the Black Capes on the Bay Chaleur shore, the 

 Silurian, in the most complete Silurian section yet known 

 in the Gaspe peninsula, is upward of 7,000 feet (2198 m.) 

 in thickness. 



The St. Alban and Bon Ami beds are sparsely fossili- 

 ferous, but the conformable Grande Greve beds of purer 

 limestone are highly abundant in species typical of the 

 earliest Devonian limestone beds, Helderberg and Oris- 

 kany At the north neither of these formations is any- 

 where well exposed except on the little Forillon peninsula 

 though both extend inward (west) into the timbered 

 heights of the northern mountain ridges. 



Two remote and detached masses of this early Devonian 

 limestone at Perce, 15 miles (27 km.) due south from the 



* There is an alternative reason to believe that the Silurian is absent at the north 

 by extinction of the deposition, but this construction of the section would only lessen 

 the amount and not the mode of destruction by the overthrust. 



