76 J. A. Dresser — Study in Metamorphic Rocks. 



deposition were crushed between the heavy masses of igneous 

 rock on either side, an apparent thickening would naturally be 

 produced by a succession of thrust planes, which owing to the 

 homogeneous character of the rock would not be easily distin- 

 guished from ordinary cleavage planes. It has been shown 

 experimentally by Cadell* that a " compressed mass tends to 

 find relief along a series of gently-inclined ' thrust planes ' 

 which dip towards the side from which the pressure is exerted." 

 This tendency, which was cited in explanation of the abnor- 

 mal thickness of the Silurian quartzites, shales and limestones 

 of Sutherlandshire, Scotland, seems quite applicable to the 

 present case, where the conditions are essentially those which 

 Mr. Cadell's experiments were designed to reproduce. The 

 uniform cleavage, which dips towards the northwest at an 

 angle of rather less then 40° for some three and a half miles, 

 may be then merely one effect of a pressure exerted from the 

 St. Lawrence vallej^ in the process of the Appalachian uplift. 



Summary. 



The results of this study are therefore to show, 



1. That the rocks of the Sutton Mountain anticline contain 

 no Precambrian elastics (Algonkian), in the vicinity of the 

 St. Francis river. 



2. That Paleozoic (Quebec Group) sediments occupy a' 

 trough between two earlier igneous ridges, viz., the serpentine 

 at the south and the trap on the north, the latter of which has 

 not been hitherto recognized in structural examinations of the 

 locality. 



3. That the Precambrian of the region, if any, is thus con- 

 fined to the volcanics, whose age has not yet been further 

 investigated since their eruptive origin has been known. 



Montreal, Canada. 



* Transactions of the Eoyal Society of Edinburgh, 1888. "Experimental 

 Researches in Mountain Building," H. M. Cadell. 



