12 



BULLETIN OF THE 



locally changed and pushed up, dislocating the surrounding sandstones. 

 The granites and sienites were regarded as probably the products of the 

 last stage of mctamorphism, although they were eruptive in their pres- 

 ent position. The *'diorites" of the Marquette district were considered 

 to be the same, in age and general characters, as the traps in the Copper 

 district, all being interstratificd with the sedimentary rocks with which 

 they arc associated, and into which they gradually pass. The differ- 

 ences between them and their associated rocks were owing to the degree 

 and manner of the metamorphism. The whole formation from the Sault 

 to the Ontonagon was regarded as Potsdam, being overlaid by the 

 magnesian limestone. 



Prof. J. P. Lesley, in his "Iron Manufacturers' Guide," (New York, 

 1859,) opposes the view of Professor Whitney, that the iron ores of 

 Lake Superior or of any other region are eruptive. It seems strange 

 that a geologist and mining engineer of his reputation should fail 

 into the errors that he has, in interpreting the latter's work. After 

 quoting Profes.sor Whitney's remarks on mineral veins, he says : " The 

 first theory which Mr. Whitney so summarily dismisses as opposed 

 to all known facts, is in certain principal localities the only one which 

 apparently embraces all the facts. The so-called veins of specular and 

 magnetic ore in Northern New York, New Jersey, and Missouri arc of 

 this class, and when Mr. Whitney says that *thc mountain masses of 

 Missouri have pre-eminently an eruptive character, and are associated 

 with rocks which have always been considered as of unmistakably erup- 

 tive origin,' we must interpret the expression by the preceding and suc- 

 ceeding paragraphs as the judgment of the past, and not his own, saying 

 that the specular and magnetic ores of Lake Superior, New York, and 

 Scandinavia fall into the same category, and yet are not true veins, but 

 'slaty beds impregnated with peroxide of iron, .... exhibiting the 

 appearance of a secondary action having taken place since their original 

 formation.'" [l. c, pp. 354, 355.) 



On referring to Professor Whitney's work, it can bo readily seen that 

 the remarks on mineral veins by Professor Whitney have nothing what- 

 soever to do with the above quoted iron-ore deposits, which arc not 

 mineral veins in any sense, and were distinctly separated from them by 

 him. The expression, *' slaty beds, impregnated with peroxide of iron," 

 was used in refc»-cnce to the mine of Hcssel, Norway, while the statement, 

 " exhibiting the appearance of a secondary action having taken place since 

 their original formation," was applied to the azoic ores of New York, and 

 ia copied by Professor Lesley on page 357 of his work in its proper con- 



