GEOLOGY OF STEEPROCK LAKE. 13 



bay where a small creek flows into Falls bay. To tbe west of the 

 creek is a carbonated green schist lying against the conglomerate. 

 This is Smyth's formation V — the ' Upper calcareous green schist.' 

 This is probably a local impure facies of the limestone or detrital 

 material that has been carbonated by reason of its proximity to the 

 limestone. 



On a small island on the east side of Straw Hat lake the rock 

 consists of a comparatively little altered volcanic ash which is 

 identical with Smyth's formation III on the west side of East bay 

 of Steeprock lake, which he refers to as a 'ferruginous formation,' 

 but describes as an impure volcanic ash. It is a soft rock, prone to 

 disintegration, and like the limestone, lies chiefly beneath the waters 

 of Straw Hat lake and in the depression which extends through 

 from Straw Hat lake to Falls bay. Between these two occurrences 

 of the volcanic ash, the one on East bay and the other on Straw Hat 

 lake, lies Smyth's formation TV, ' Interbedded Crystalline traps.' 

 This I found to consist very largely of rather massive green schists 

 of detrital origin, with abundant angular fragments of quartz, 

 traversed parallel to the strike by what appeared to be great dykes 

 of diabase, but which may possibly be massive flows. 



On the east side of East bay the fonuations are as Smyth 

 described and mapped them, viz. : a basal conglomerate, I, of quite 

 moderate thickness, resting on the granite gneiss of the east shore, 

 followed to the west by bedded limestone, II, for a thickness of 

 several hundred feet, the whole in nearly vertical attitudes. 



From the facts above stated, it is evident that in a section 

 transverse to East bay and Straw Hat lake we have to deal with a 

 twofold repetition of the same set of beds; and the unavoidable 

 conclusion is that the structure is a simple, closely folded syncline. 

 The three lowest formations of the Steeprock series as described 

 by Smyth on East bay are repeated on Straw Hat lake in reverse 

 order. The duplication of formation IV has not been made out, 

 and it is doubtful if it can be, owing to the character of the rocks, 

 which renders it difficult to distinguish one horizon from another, 

 and to the dykes which cut it. The conglomerate VI is, therefore, 

 the same as I, and it is a basal conglomerate resting upon the 

 Keewatin. This conglomerate was deposited upon an eroded surface 

 across the contact of the Keewatin and the granite gneiss. The 

 insunken syncline happens to cover the contact, so that on one limb 

 16279— 3i 



