THE LOWER HURONIAN. 351 



amygdaloidal lavas, and here the top layers of the Upper Slate are the 

 ordinary or slightly metamorphosed black slates. From this it appears 

 clear that on the Penokee range the metamorphism of the slates and mica- 

 schists is dne to the gabbro, and the same conclusion seems to follow for 

 the similar schists in the Vermilion district. 



The Lower Huronian slates appear at a number of places on the 

 north, south, and southeast shores of Gobbemichigamma Lake. On the 

 southeast and east shores these slates are in many places found in direct 

 contact with the Keweenawan gabbro, and where near it or in contact with 

 it they have been extremely metamorphosed. Much less metamorphism is 

 noticeable on the slates occurring on the north side of the lake. That part 

 of the south shore of the lake in the immediate vicinity of the section 

 line between sec. 1, T. 64 N., E. 6 W., and sec. 6, T. 64 N., R. 5 W., affords 

 a good opportunity for studying the relations between these two rocks. 

 There is a high cliff at the point where the section line above mentioned 

 comes to the shore. On this cliff one can readily detect bands of rock 

 which strike N. 10° E. magnetic and dip 20° to the east. This strike as 

 taken really represents the strike of the face of the cliff. Were it possible 

 to obtain it, the true strike of the beds would be found to be somewhat dif- 

 ferent. The bands in the cliff are made up of very dense-grained, hard, 

 siliceous rock. They are rarely more than 4 inches in thickness and fre- 

 quently very much thinner. Alternating with these bands there is a 

 rotten, brown, coarse-grained material which seems to weather very 

 readily — it certainly does so in comparison v/ith the adjacent harder 

 bands — and appears much like gabbro. If we follow the shore around to 

 the northeast it is there possible to land and ascend the sloping hill leading 

 to the top of the above-mentioned cliff. In the ascent of this hill one 

 crosses the bands of rock, which are imperfectly shown in this section. 

 The harder bands are especially recognizable, as they are likely to form 

 shelves, the slopes between being formed of the softer gabbro-like material. 

 The relations here seem to indicate either that the banded sedimentary has 

 been included in the gabbro or else that the gabbro has been thoroughly 

 injected into the sedimentary, the injection following chiefly the bedding 

 planes as planes of least resistance. The normal coarse-grained gabbro 

 occurs on the shore just a short distance — about a quarter of a mile — back 

 of this headland. Following this shore from the cliff to the west we note 



