THE GEOLOGY OF STEEPROCK LAKE, ONT. 



BY 



Andrew C. Lawson. 



lu the year 1891, Mr. H. L. Smyth published an interesting 

 paper' on the geology of Steeprock lake, in which he classified the 

 rocks there exposed into three principal groups : — 



(1) The Basement Complex, consisting of granites and gneisses 

 which typically are medium grained, hornblendie and granitoid 

 with faint foliation. Locally they present considerable variations 

 in composition and very great variations in structure. 



(2) The Steeprock series, showing a thickness of 5,000 feet. 



(3) The Atikokan series, a succession of later granitoid porphy- 

 ries and massive hornblende rocks. 



The Steeprock series rests unconformably upon the basement 

 complex, and is subdivided into nine formations, according to the 

 following scheme, arranged in ascending sequence : — 

 I. Conglomerate. 

 II. Lower limestone. 

 III. Ferruginous formation. 

 IV. Interbedded ery.stalline traps. 

 V. Upper calcareous green schist. 

 VI. Upper conglomerate. 

 VII. Greenstones and .creenstone schists. 

 VIII. Agglomerate. 

 IX. Dark grey clay slate. 

 The sequence of these formations and their structural relations 

 formed the chief subject matter of Mr. Smyth's paper, and the 

 discussion of his third division, the Atikokan series, was deferred. 

 The paper was not only interesting, but it was important from a 

 general point of view as an announcement and description of a 



» Structural Geology of Steeprock lake, Ontario, Am. Jour. Sc. XLII, 

 1891. 



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