48 Dresser — Contribution to the Geology of Quebec, 



in the vicinity are made up of its debris. Other evidences 

 also point to the later age of the sedimentary rocks, which 

 generally belong to the Trenton formation, and none to 

 the reverse relation. The change of view in regard to the 

 origin of these rocks, from sedimentary to igneous, does not, 

 therefore, necessarily alter the recent determinations either of 

 their relative or of their actual geological age. It would, 

 however, be well that the evidence on which the latter deter- 

 mination was made should be carefully reviewed in the light 

 of the present knowledge of their volcanic character. 



On the other hand, the elimination of these volcanics leaves 

 the stratigraphical structure of the sedimentary rocks a much 

 simpler one than has hitherto been supposed. 



A detailed study of the Sutton belt and adjacent forma- 

 tions in the vicinity of the St. Francis river shows the sedi- 

 mentary rocks of the Quebec Group to occupy a trough be- 

 tween the volcanic ridge on the north and the serpentine belt 

 at the south. Both these have apparently been covered by 

 sediments which are now in part removed by denudation. 



A surnmary of the results of this study, therefore, shows : 



1. That at least the greater part of the pre-Cambrian or 

 crystalline belts of the eastern townships of Quebec is of 

 igneous, not sedimentary origin, as has been hitherto sup- 

 posed. 



2. That these rocks are allied to the volcanics of South 

 Mountain, Pennsylvania, especially to the basic types, and 

 indicate the continuance of this class of rocks throughout the 

 Appalachians, as was suggested by Williams. 



3. That the sediments of the region, which probably all 

 belong to the Quebec Group, were deposited between and 

 upon the preexisting ridges of igneous material, which are 

 now being uncovered by denudation, while the intervening 

 valleys still remain deeply filled. 



The pre-Cambrian area near the international boundary line, 

 before referred to, and also the extension of the Sutton belt 

 into the State of Yermont, would furnish subjects of investi- 

 gation of especial interest in connection with the areas herein 

 described. 



Eichmond, Quebec, Canada. 



