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THE LAKE SUPERIOR SYNCLINAL. 415 
Bay, and in the rock belts composing them, a similar curvature to the south 
of east is begun. That this continues until it becomes nearly or quite a 
southerly course is shown by the trend of the northeast coast line of the 
lake, which is composed of the older rocks, between the Pie and Michipi- 
coten Island, where the Keweenawan rocks again appear. The parallelism of 
the northeast coast, of the line marked out by the eastern end of Keweenaw 
Point and Stannard’s Rock, and of the south coast between Keweenaw 
Bay and Marquette, looks also the same way. 
Still further to the east, the South Shore shows only rocks newer than 
the Keweenawan, but at the east end of the lake a continuous belt of the 
latter rocks is marked by Michipicoten Island, Capes Choyye and Gargantua, 
Pointe Aux Mines, the peninsula of Mamainse, the coast of Batchewanung 
Bay, and Gros Cap, the beds always dipping lakeward. The most striking 
thing about this belt is its parallelism to the lake coast behind it, and the 
consequent abrupt turn, at more than right angles, in the Michipicoten 
bight. 
In the map of Plate XX VII and the accompanying sections of Plate 
XXIX, I have attempted to summarize the facts bearing upon the subject 
of this chapter, and to generalize from them to the structure of the syn- 
clinal. The spaces between the red lines of this map are each supposed 
to represent 2,500 feet of rock thickness, the spaces being narrow where 
the dip is high, and correspondingly broad where it is low. The lines were 
constructed by first platting out the spaces in those districts where actual 
measurements had been made of strike and dip, the width of each space 
being made to correspond to the width of the surface outcrop of a 2,500- 
feet thickness at the measured angle of dip. Where actual thinning on a 
large scale had been proved by careful measurement to exist—e. g., on 
Keweenaw Point—the lines were approached on this account also to the 
determined amount. Then the broken connecting lines were sketched in, 
taking into account the general lithological characters of different horizons 
—often recognized for over a hundred miles—the relations of the belts to 
the junction with the Huronian below and to the line between the Upper 
and Lower Divisions of the Keweenawan, and the angles of inclination and 
trends indicated by the nearest exposures. 
