THE STEEP ROCK SERIES. 345 



A folded Syncline. — The discovery of a well-marked band of brownish 

 gray clay slates very similar to those on the shore of Steep Rock lake, 

 striking in an easterly direction and dipping to the north, though at high 

 angles, which lie about a mile and three-quarters south of the southern 

 bend of the lake, and which would seem to represent the southern upfold 

 of the horizon (IX), would indicate that the series must he regarded 

 rather as a folded and buckled syncline than as a tilted and buckled 

 monocline. This simplifies the conception, as it answers the somewhat 

 troublesome question as to what has become of the corresponding half 

 inferred by the supposed monocline. The country south of the middle 

 bend of Steep Rock lake and lying between its western and eastern long- 

 extending arms is extremely rugged and is almost impassable, so that 

 the sequence of the rocks could not be worked out. 



Its Thickness. — If the conclusions drawn from the discovery of the clay 

 slates south of the lake are just, the higher horizons inferred by Smyth 

 seem to consist principally of coarsely crystalline traps and light greenish- 

 gray, close-textured traps, with their schistose mechanical derivatives 

 paralleled by horizons IV and VII. and about 4,000 feet must he added 

 to the total thickness of the series as estimated by Mr Smyth. 



Its Relation to the Laurentian and Keewatin. — This extensive series ap- 

 pears to have been laid down upon the eroded surface of the Laurentian 

 and Keewatin rocks long after the irruption of the Laurentian granites. 



Effect upon it of orographic Movement. — It appears, then, as pointed out 

 by Smyth, to have been folded by crustal movements into a cynclinal 

 trough, whose axis had a northwest and southeast direction. Subsequent 

 to this ;i great lateral pressure, acting in a direction nearly parallel with 

 this synclinal axis, has buckled the whole series in a horizontal plane 

 and crushed and sheared the underlying basement rocks. Relief from 

 this pressure was also afforded by a slipping of the rocks in the vicinit}' 

 of Northwest bay of Steep Rock lake, indicated by a complicated series 

 of faults which are clearly recognizable in the Steep Rock series and may 

 be inferred by the distribution of the Laurentian and Keewatin rocks to 

 the north and to the south. These faults indicate a horizontal disloca- 

 tion of nearly 7,000 feet in the aggregate, and that the vertical dislocation 

 must have been of even greater extent is inferred by the volume of these 

 newer rocks which were faulted below the present level of denudation. 



Older than the Animikie. — The lateral pressure which produced these 

 faults and the remarkable structure of the Steep Rock series acted in a 

 northwest and southeast direction, and it is most highly probable that 

 it was the same pressure which, acting from a center of force to the south- 

 east, produced the lenticular character of the granitic areas referred to in 

 an earlier part of this paper. As the Animikie rocks northwest of Lake 



