RELATION OF TOPOGRAPHY TO STRUCTURE. 433 



glomerate come anticlines of Archean rocks. Mud Creek, about a mile and 

 a half north of Armstrong Bay, flows also in a depression occupied by the 

 Lower Huronian sediments, which are flanked by Archean greenstone. 

 Similar cases are shown in the synclines of sediments extending from Ver- 

 milion eastward to Bass Lake, in sec. 2, T. 62 N., R. 15 W , and extending 

 eastward along Rice Bay of Vermilion Lake, in sees. 34 and 35, T. 63 N., 

 R. 15 W., still farther north. 



In T. 64 N., R. 9 W., Moose Lake occurs, lying in a syncline of Lower 

 Huronian slates. On the west side of the northern bay of Moose Lake, 

 that one out of which the portage to Wind Lake goes, the salient on the 

 west side is formed by an Archean greenstone anticline with reentrants on 

 both sides in the Lower Huronian slates. Knife Lake shows a beautiful 

 case in the 2-mile long point of Archean greenstone projecting west 

 through sees. 22 and 23, T. 65 N., R. 7 W. Both to the north and south of 

 this erosion has very nearly removed all of the Lower Huronian sedi- 

 ments from contact with this anticline, small patches only being found on 

 the north and south flanks, as shown on the geologic maps in the accom- 

 panying atlas. Lake Gobbemichigamma, in sees. 31-32, T. 65 N., R. 5 W., 

 and sec. 6, T. 64 N., R. 5 W., and sec. 1, T. 64 N., R. 6 W., lies right at the 

 junction of three great formations and is influenced in its shape very 

 markedly by them. On the shores each formation shows the toiDographic 

 forms characteristic of it. The formations meeting here are the Archean 

 gi-eenstone and the Lower Huronian Knife Lake slates, which overlap 

 upon the greenstone, and in contact with both of the above and over- 

 lapping them is the Keweenawan gabbro. The Twin Peaks Archean 

 anticline forms a bold east-west ridge, the end of which overlooks the 

 lake and projects into it from the west, forming two salients. The slight 

 embayment to the north of this greenstone is along the contact of the Archean 

 and the Lower Huronian slates, while the embayment to the south follows 

 a little to the south of the contact of the Archean greenstone and of the 

 Keweenawan gabbro. The greenstone runs down in a very steep slope to 

 the water. The north side of the lake is bounded by the slates, and here 

 there is a gentle slope down to lake level. On the southeast and south sides 

 of the lake the gabbro appears in steep cliff's and prominent headlands, the 

 irregularities of the shore being influenced in their trend by the marked 

 jointing of the gabbro. 



MON XLV— 03 28 



