PROCEEDINGS OF THE CANADIAN INSTITUTE. S:; 



Note on Some Basic Dyke and Volcanic Rocks of Eastern Ontario 

 AND Quebec. By W. G. Miller, M.A. 



(Read April i8, 1897). 



Dr. F. D. Adams, in his recently published " Report on the Geology of a Portion 

 of the Laurentian Area Lying to the North of the Island of Montreal " (i), describes 

 a series of post-archiean dykes which are stated to be " probably pre-Poisdatn 

 in age." The rocks in these dykes are of three different kinds, viz. : diabase, augite 

 porphyrite (spilite type), and a rock which " is neither a diabase nor a gabbro, 

 having neither the ophitic structure of the former nor the hypodiamorphic granular 

 structure of the latter. The structure is rather a porphyritic one . . ." 



It may be interesting to note that 'a similar series of basic rocks occurring in 

 dykes is characteristic of the Kingston district, which is distant about 150 miles from 

 the area referred to by Dr. Adams. 



In a paper (2), published some time ago, Mr. R. W. Brock and the present 

 writer described two rocks which with diabase are the 'characteristic basic dyke and 

 volcanic rocks of the eastern part of Frontenac county and the adjacent portions 

 of the counties of Leeds and Lanark. One set of dykes, which occurs near the village 

 of Seeley's Bay is, judging from Dr. Adams' description, practically identical in 

 character with those he has described in the district north of Montreal, and which 

 he calls augite porphyrite (spilite type). 



The rock referred to by Dr. Adams as being " neither a diabase nor a 

 gabbro " is represented in the Kingston district by a rock which resembles 

 it closely. The Quebec rock is apparently somewhat more basic than its 

 Kingston representative, and contains phenocrysts of both augite and plagio- 

 clase, of which the former is the older. Unless, however, a series of analyses 

 were made of specimens selected from dififerent parts of the dykes, it would not be 

 possible to make a satisfactory comparison of the ascidity of the dykes in the two 

 districts. One of the striking characteristics of these rocks from both districts is 

 the occurrence in them of micropegmatite or a granophyric intergrowth of quartz 

 and feldspar. Dr. Adams says, " This micropegmatitic or granophyric intergrowth 

 of quartz and feldspar will probably be found very widespread in its occurrence in 

 the dykes cutting the arch;ran in Canada, as it is known in diabases of Templeton, 

 in the County of Ottawa, in the Province of Quebec, while Dr. Lawson describes it 

 as occurring abundantly in the dykes of the Rainy Lake district to the west of 

 Lake Superior." 



Prof. C. H. Smyth has described a group of diabase dykes among the Thousand 

 Islands, St. Lawrence River, in the southern part of the County of Leeds (3). 

 These also have representatives in the area described by Dr. Adams. 



Dififerent varieties of plutonic rocks related to gabbro are found in the two 

 districts. Letting the term gabbro stand for these, norite and anorthositc. we have 

 an interesting series of rocks in the two districts, including — if we consider the rock 

 containing micropegmatite to belong to the dyke division proper — plutonic, dyke 



(i) Pp. 134 to 139, Part J. Annual Report. Vol, VIII., Geol. Survey of Canada. 



(2) Canadian Record of Science, October, 1895. 



(3) Transactions N.Y. Academy of Sciences, Vol. XIIL 



