■Til 



80 



BULLETIN OF THE 



United States," presents the metamorphic theory of the origin of the 

 rocks of Keweenaw Point as follows: "The rocks of Copper Harbour, 

 and indeed of the whole Kewenon peninsula, are decidedly metamor- 

 phic, showing every degree of change produced by igneous agency, from 

 unchanged sandstone to compact greenstone. The stratification is, 

 mostly, more or less evident, presenting in the various superimposed 

 layers, an inexplicable variety, some layers bearing evidence of 8cuii- 

 fusion and a correspondent degree of induration and endurance, while 

 others seem scarcely to have been altered, still remaining soft and yield- 

 ing readily to atmospheric 'agency, and especially to the assaults of the 

 ■waves from the lake. Whether these differences have been produced 

 by an nnecpial distribution of the heat, or by an original difference in 

 the layers of the strata, some being of a nature more susceptible of 



change by heat, I was unable to determine Copi)er Harbour 



itself seems to have been formed by the removal of a softer stratum 

 of metamorphic sand rock, while Porter's Island is a part of the barrier 

 formed by the outcropping of a harder layer." {L c, pp. 311, 312.) 



In 1845,* Lieut. D. Rugglcs published a communication in which 

 he advanced the view that the trap was projected in dikes through the 

 New Red Sandstone, and that the veins were formed and fdled " by vol- 

 canic or igneous action, under the pressure of incumbent waters." If 

 ■we can judge from his statements about the copper and his description 

 of the filling of the veins in the "Lead Region " of Illinois, Wisconsin, 

 and Iowa, he believed that these veins were filled by the projection of 

 metallic copper, enveloped in a dense atmosphere of oxygen "from the 

 fountain of igneous action, through fissures in the rock strata, resulting 

 from concurrent disturbing causes." When the vein was "under the 

 pressure of an immense mass of water," the oxygen entered into com- 

 bination with the copper to form the black oxide of copper, but when 

 only under atmospheric pressure the oxygen escaped by sublimation, 

 leaving the copper to its own resources. 



Dr. Chas, T. Jackson, writing in 1845,t regarded the sandstones as 

 probably Permian or New Red, but attributed to Dr. Houghton the 

 belief that the formation is Old Red, and also held that the trappean 

 rocks were injected dikes. The veins were taken as veins of igneous 

 injection, although doubt is expressed, and he says : " When these veins 

 occur near the trap dykes, analcime and Prelmite also abound, and were 

 formed, without doubt, through the igneous agency of the trap on the 

 contents of the vein and the ingredients of the wall rock." AVe may 



* Am. Jour. Sci., (1,) XLIX. 62-72. 



t Ibid., pp. 81-93. 



