MUSEUM OF COMPAKATIVE ZOOLOGY, 103 



" The veins of the district were of course formed long after the con- 

 solidation of the beds, and probably when they were being lifted into 

 their present position. They have subsequently been filled with the 

 various minerals which now occupy them, wholly by infiltration and 

 chemical, probably aided by attendant electric, action, and in a system- 

 atic and natural sequence." (/. c, pp. 108- 115.) 



Regarding the junctions of the sandstone and amygdaloid in two local- 

 ities he says: " J n?ic( ion, very irregnhxr. For two feet the underlying 

 sandstone is changed and indurated, being, in places, hardly distinguish- 

 able from the overlying mclaphyr, except for enclosed pebbles which are 

 not changed. Some pebbles rest upon the hanging-wall, which are quite 



enclosed in the overlying amygdaloidal melaphyr Junction, slightly 



undulating. No change or metamorphism in the adjacent beds. Extend- 

 ing from the junction down into the underlying melaphyr — about 

 eight feet being exposed — is a fissure or crack with sharply defined 

 edges and two abrupt bends, giving widths of two and four inches. This 

 crack is filled with sandstone similar to that above, but somewhat finer 

 and slightly decomposed or softened. There is an appearance of iiTegu- 

 lar, but rudely curved stratification, about parallel, as a whole, with 

 the formation." (/. c, pp. 118, 119.) 



It is to be seen, then, that Mr. Marvine arrived at the same con- 

 clusions regarding the Copper-bearing rocks as did Messrs. Foster and 

 Whitney, and supported these views by the same evidence that they 

 had more fully and thoroughly given in their report. 



In Part III.* we have the report of Dr. C. Rominger on the Palaj- 

 ozoic Rocks. Regarding the sandstone he says : " The lower Silurian 

 age of the Lake Superior sandstone is unequivocally proved by its 

 stratigraphical position. In its whole extent it is visibly overlaid by 

 calcareous ledges, containing fossils peculiar to the Caleiferous forma- 

 tion, or, in other cases, by the Trenton limestones. The recognition of 

 a separate rock-series, identifiable with the Caleiferous formation, at 

 once nullifies the other mentioned opinions of Geologists, and leaves no 

 choice but to see in the Lake Superior sandstone the equivalent of the 



Potsdam sandstone The thickness of the Sandstone formation is 



difficult to ascertain. Its lower portions are so intimately connected 

 with the sandstones and conglomerate beds of the coi)por-bearing Trap- 

 pean series, that I could draw only an arbitrary division line between 

 the two groups, which would swell the thickness of the sandstone group 

 to many thousand feet, while east of the Copper range, the whole sand- 



* Geol. of Mich., I. 1873. 



