Dresser — Contribution to the Geology of Quebec. 47 



(b) The igneous origin of a portion of the pre-Cambrian 

 area, which forms the Sutton Mountain belt^ was pointed out 

 by the writer in a note to the Ottawa Naturalist of January, 

 1901. Since that time the extent of the igneous portion has 

 been more fully examined, especially to the northeast of the 

 St. Francis river, and its structural relations better ascertained. 

 It is found to comprise the greater part of the pre-Cambrian 

 of this area, as shown on the latest geological survey map of 

 the region, that of 1886. 



As far as examined, for a distance of some forty miles on 

 either side of the St. Francis river the rock is an altered 

 greenstone, very commonly amygdaloidal. In the microscopic 

 section a little primary plagioclase sometimes remains, but in 

 many sections the whole field consists of a secondary aggre- 

 gate of chlorite, epidote, iron ore and leucoxene. The amyg- 

 dules usually consist of quartz and zeolitic minerals. The 

 rock is much foliated and has been generally described as a 

 chloritic slate. Its resemblance to the basic rocks of the Ascot 

 area is very close. It, too, is important as a copper-bearing 

 rock. 



In geographical position these volcanic belts form a link in 

 the more westerly of the two chains of ancient volcanics des- 

 ignated by the late Prof. G. H. Williams,"^ while in their 

 lithologic characters they agree with certain of the South 

 Mountain rocks of Pennsylvania in all essential respects. f 

 The Quebec rocks are, however, largely made up of the acid 

 types, some of which agree essentially with rocks from Ascot. 

 Most of the specimens are in less advanced stages of recrys- 

 tallization than the rocks above described. 



The basic phases from the Stoke Mountain area as well as those 

 which comprise the Sutton Mountain belt are closely analogous 

 to the greenstones from the vicinity of Monterey. 



Steucture. — As already stated, these rocks were formerly 

 regarded as presenting synclinal structures, while the later 

 investigators have believed them to form anticlines, the former 

 view making them later in age than the adjacent rocks, the 

 latter, earlier. With respect to relative age, the latter opinion 

 is doubtless the correct one. The lowest sedimentary rock, 

 dolomite, on the south side of Sutton Mountain belt in 

 the township of Melbourne, for instance, contains fragments 

 of the adjacent trap, and large areas of mica schists 



* The Journal of Geology, Jan. -Feb., 1894. 



t A collection of rocks from this locality, which is in the petrographical 

 laboratory of McGill UniYersity, has been examined for comparison 

 through the courtesy of Prof. F. D, Adams, to whom my best thanks are 

 also offered for valuable aid and advice in several matters connected with 

 this subject. 



