1880 .] 
103 
[Wadsworth. 
taneously it was carried to some extent into the adjoining sandstone.” 
(Am. Jour. Sci., 1880 (3), xx, 331, 332.) 
These extracts speak for themselves, and comment by me is 
unnecessary. 
It may further be pointed out that Professor Dana is only 
partly correct in stating that I “ make the iron ores and associated 
beds of jasper intrusive .” I hold that they are chiefly eruptive, 
partly intrusive, partly in overflows; also formed in part by 
decomposition of the jasjnlite and ore in situ , and in part by 
mechanical and chemical deposition. (See Proceedings of this 
Society, 1880, XV, 470-479.) 
Again Professor Dana says : 
“ The sandstones and conglomerates which accompany the trap in the 
copper region, and are more or less interstratified with it, owing to suc- 
cessive deposits and outflows, as described by Whitney, are pronounced to 
be of the age of the Potsdam sandstone; but the conclusion is not based 
on the writer’s personal observations.” 
Professor Dana’s meaning is somewhat obscure here. If he 
means the conclusion that the copper-bearing traps, sandstones, 
and conglomerates were of the same age as the sandstone shown 
to be Potsdam by Messrs. Foster, Whitney, and Rominger, is 
not based on my personal observations he is mistaken. The 
present writer’s personal observations showed that which had 
never been observed before, that the copper-bearing rocks were 
interstratified with the eastern sandstone (Potsdam of Foster, 
Whitney, and Rominger; New Red, Potsdam and Calciferous, 
and Calciferous of Dana) and were continuous with it, although 
it was held by the majority of geologists that the copper-bearing 
rocks were older (pre-Paleozoic) than the eastern sandstone 
(Paleozoic) and underlying it. If Professor Dana means that I 
did not by personal observations show that the eastern sandstone 
wms Potsdam in age he is correct. It was not a problem before 
me since Dr. Rominger’s evidence until shown to be incorrect is 
conclusive. (See Proceedings of the American Association, 
1880 : “ On the Age of the Copper-bearing Rocks of Lake 
Superior.” 
