X CONTENTS. 



* 



of Switzerland distinct, and the materials in well- determined order, 

 396. Similar phenomena observed in other parts of Europe, 396-7. 

 Points necessary to be settled ; first, the relation in time and character, 

 between the Northern and the Alpine erratics, 397. Traced in North 

 America, 397-8. Not yet settled whether any local centres of distribu- 

 tion in this country ; but the general cause must have acted in all parts 

 simultaneously, 398. The action ceased at 35 north latitude; this 

 incompatible with the notion of currents, 399. In both hemispheres a 

 direct reference to the polar regions, 400. Difficulty as to so extensive 

 formation of ice, removed ; difficulties on the theory of currents, the 

 effects contrary to experience of water-action, 401. Erratic phenomena 

 of Lake Superior, 401-4. The iceberg theory, 405-6. Description of 

 appearances at Lake Superior, 406-9. Drift; contains mud, and is 

 without fossils, 409. Example of juxtaposition of stratified and un- 

 stratified drift, at Cambridge, 410. Date of these phenonema not fully 

 determined, but doubtless simultaneous all over the globe, 410-411. 

 The various periods and kinds of drift distinguished, 412. Accompanied 

 by change of level in the continent ; terraces at Lake Superior, 413-14. 

 Not from a subsidence of the water, but from upheaval of the land, 

 414-416 , 395-416 



XI. 



THE OUTLINES OF LAKE SUPERIOR. 



The present physical state of our globe the result of gradual and suc- 

 cessive changes, 417. Necessity of studying out in detail minor and 

 secondary phenomena, 418. Position and general features of the Great 

 Lakes, 419-20. Lake Superior; the dykes correspond in direction with 

 the trend of the shores, 420. Details, 421-2. Enumeration of the 

 various systems of dykes, 423-4. These dykes have cut up the primi- 

 tive formations so as to produce the present outlines of the lake, 424-5. 

 The rocks of Lake Superior as evidence that the erratics of more 

 southern localities were derived from the primitive range extending 

 north of the lakes to the Atlantic, 425-6 417-426 



XII. 



GEOLOGICAL RELATIONS OF THE VARIOUS COPPER DEPOSITS OF LAKE SUPERIOR. 



The distribution of the copper ores at Lake Superior, as indicating 

 their origin ; the native copper plutonic and unchanged near the centre 

 of eruption, but modified and combined at a distance, 427-428 



