30 ON THE FRESH-WATER GLACIAL DRIFT 



the island, a distance of sixty miles. Siskowit harbor, Rock harbor, Washington 

 harbor, and Tod harbor are exact imitations of those on Point Keweenaw. In the 

 interior, between the ridges, at all elevations above the lake, to the summit of the 

 island five hundred and six hundred feet, are long narrow lakes, the longest axis 

 being, as usual, parallel with the outcrops of the rocks. These rocks are more 

 denuded than upon Point Keweenaw, and are everywhere rounded, scoured, and 

 striated. To the west and southwest, along the north shore of Lake Superior, the 

 rocks have nearly the same strike, and dip towards the south and southeast, but 

 were not as thoroughly exposed to the drift forces, owing to a mountain range on 

 the north, ten to fifteen miles distant. 



The northerly and northwesterly faces of the highlands received the first and 

 greatest pressure. To the south of Point Keweenaw, in Marquette county, is 

 repeated what had occurred on Isle Royal. The islands, and rocky points, headlands 

 and islets around Presque Isle bay. Riviere Des Morts, and the village of Marquette 

 are thoroughly ground down to dome-shaped surfaces, with warped floors, troughs, 

 grooves,, furrows, and striae, the general course of which is. southwesterly. 



Here the strike of the' strata is nearly east and west with less difference in the 

 beds as to hardness. On the coast north of Marquette there are outbreaks of sienite 

 and granite, which did not resist the movements so well as the trap and iron beds. 

 The quartz strata and the marble beds are less aff'ected than the azoic slates, but 

 are aU highly polished, the exceedingly fine strise etched thereon remaining almost 

 as perfect as they were when the icy graver finished, its work. 



On the summit, there are the Teal and Matchigummi lakes, surrounded by the 

 same evidences of ice action ; but their form has not been as much changed by it 

 as those on Isle Royal. To the northwest of Lake Superior, along the line of Pigeon 

 river and Rainy lake river, this action is Very conspicuous. Vermilion lake, 

 which is in the Mesabi range, is surrounded by gneiss, granite, and slates, having 

 a northeasterly and southwesterly trend. 



Rainy lake has a geology very simdar. Both of them present a labyrinth of 

 islands, inlets, bays, straits, and harbors of the most interesting and complicated 

 character. The rocks are not bold, but mostly divested of earth, and thoroughly 

 abraded. On the softer portions, such as recent granite and talcose slates, the 

 effects are visible only in the smooth dome-like moutonnes, without strise ; but on 

 the quartzose portions the markings are yet distinct. But we must extend our 

 ideas of glacier excavation to larger bodies of water. The basins of the North 

 American lakes, constituting the valley of the St. Lawrence, have been modified by 

 the same agent. By consulting the accompanying map, it Avill be seen that the 

 direction of the movement was in general along their longest axes. 



It is remarkable that most of them have the long axis nearly in the directions of 

 the bearing of the rocks. In some cases, the strata which have least resisting 

 power lie at the bottom of a lake ; and more than this, the course of the arrows 

 shows that the glacier moved along the outcrop of these beds, having the same gen- 

 eral direction, thus combining all the circumstances favorable to erosive effect. 



At the bottom of Lake Ontario are the rocks of the New York system, from the 



