Wadsworth.] 
96 
[November 17, 
cult to see any foundation for the hypothesis of Professor Dana 
concerning the veins, as advanced in the editions of 1862 and 
1874. Although the veins in the Ontanogon district are said 
to be contact veins, the veins in the district visited by me, 
and under discussion here, are not contact veins, but, as said 
above, cut directly across the beds of trap and conglomerate. 
The material filling a fissure, whether it be a dike or vein, shows 
by its structure, relations to the country rock, and other charac- 
ters, how the fissure was filled. That the veins in the district in 
question are neither veins of injection nor of sublimation has been 
so conclusively shown in the works of others, that it need not be 
touched upon here, further than to remark, that not a single char- 
acter was seen in the veins studied by me that pointed towards 
either injection or sublimation. The writer is, therefore, unable 
to see that, in the district in question, there is any basis for Pro- 
fessor Dana’s views advocated in the edition of the Manual for 
1880. 
While I would not deny that in certain cases, in other localities, 
Prof. Dana’s hypothesis may explain all the phenomena and per- 
haps be the correct view, I feel in the light of the facts given 
above and elsewhere, that it is untennable as respects the dis- 
trict in question. I take this ground too, with all respect for the 
opinions and labors of Prof. Dana, from whose Text Book of 
Geology, I gained my first conceptions of that science and of the 
formation of Mineral Veins. 
Prof. Dana is unquestionably the best authority regarding his 
own views, but I feel that he is mistaken in his statement 
that his present views were advanced in the American Jour- 
nal of Science in 1845 (XL1X, 49-64), and that he has always 
held the same theory “only slightly modified,” as that presented 
in the October number of the American Journal. In order to 
show this, as well as to reply to his more general statements, I 
shall quote at some length from his writings, which in many cases 
uphold my position far better than I can myself. 
“ Minerals occupying cavities and seams in amygdaloidal trap or basalt . — 
These minerals have been attributed to a variety of sources, and even at the 
present time there are various opinions respecting their origin. According 
to some writers, they result from the process of segregation; — that is, a 
separation of part of the material of the containing rock during its cooling 
