397 



to the Carboniferous o;roup of rocks, and are of the genus Paleonis- 

 cus, and similar to those found in the European coal formations ; 

 but there are no fossil fishes in the coal-mines of the Joggins 

 in Nova Scotia, and hence no local comparisons could there be 

 made. 



As to the geological age of the sandstones of Keweenaw Point, 

 Lake Superior, Dr. Jackson, in his Report to the United States 

 Government in 1849, had presented all the facts and considera- 

 tions then known, to solve the question, and in his arguments 

 rather favored the idea that they were of Triassic age, and that 

 they were certainly coeval with the sandstones of Nova Scotia, 

 Connecticut River, and New Jersey, as proved by their paral- 

 lelism on De Beaumont's system, — identity of composition, — 

 mode of disruption, — characters of associated minerals, and, 

 above all, by the fact that they rest upon . Devonian limestones, 

 exactly as do those of Maine and Nova Scotia. Still, since some 

 difference of opinion on this subject was known to exist among 

 geologists who had visited Lake Superior, Dr. Jackson, in his 

 geological maps of the copper regions of that country, had simply 

 denoted those rocks as Red Sandstone of Lake Superior. 



The discovery of an Orthoceratite at the Copper Falls mine, 

 and of a Pentamerus in the underlying limestones of Sturgeon 

 River, absolutely demonstrate that the sandstones of Keweenaw 

 Point are not Potsdam, and the occurrence of pebbles of Pitch- 

 stone Porphyry in the conglomerate of Isle Royale indicates, so 

 far' as mineral components can be relied upon, that those conglom- 

 erates are more recent than those of the Isle of Arran in Scot- 

 land, set down as Triassic by Prof. Sedgwick, and now regarded 

 as Devonian. 



The strong geological and mineralogical resemblance between 

 the copper regions of Lake Superior and those of Nova Scotia, 

 New Jersey, and Connecticut, cannot fail to strike every one who 

 has compared them. The identity of the concomitant minerals in 

 the amygdaloid and trap breccias, and in the native copper veins 

 of all these localities, proves similarity of conditions in their 

 formation and of the rocks which produced them. Direct com- 

 parisons between the Lake Superior sandstones and the copper- 

 bearing sandstones and t^hales of Germany by Mr. Marcou seem 

 to have set the question of the geological age of these rocks 



