THE 



CANADIAN NATURALIST 



AND 



NOTES ON A FEW DYKES CUTTING LAURENTIAN 

 ROCKS, MORE ESPECIALLY WITH REFERENCE 

 TO THEIR MICROSCOPIC STRUCTURE. 



By B. J. Harrington, 

 Of the Geological Survey of Canada. 



The fact that rocks of Laurentian age are frequently cut by 

 trap dykes, was many years ago noticed by Sir William Logan, 

 who traced out and mapped a number of those found in Greu- 

 ville and some of the neighbouring townships. Since then other 

 observers have noted their occurrence in widely distant Lauren- 

 tian areas. Mr. Vennor, for example, observed dykes in Madoc 

 and North Burgess. Mr Macfarlaue in his report on Lake 

 Superior * describes dykes which cut the Laurentian rocks at 

 Goulais Bay, Gros Cap, and other localities, and from his de- 

 scriptions some of them appear to resemble those found in Gren- 

 ville. At Goulais Bay they are from nine to seventy feet thick, 

 strike N. 72° to 75° W., and are probably doleritic. Others at 

 Gros Cap and the mouth of the Montreal River Macfarlane also 

 considers to be dolerites, but states that near Michipicoten Har- 

 bour, and in Bachewahnung Bay, there are dykes of diorite. 

 He further states that at two different points in the Laurentian 

 area examined by him, he observed intrusive rocks of the 

 character of the " newer traps or melaphyres which characterise 

 the upper copper-bearing series." 



* Geology of Canada, 1866, p. 120. 

 Vol. VIII. u No. 9. 



