1880.] 
95 
[Wadsworth. 
trap. These veins are true fissure veins, and they affect the 
amygdaloidal and copper-bearing character of the old basalts 
to such an extent that I doubt not that the veins and cavi- 
ties were filled contemporaneously with the alteration of the 
basalt. In some mines the trap is heavily copper-bearing in 
juxtaposition to the veins, and contains but little copper a short 
distance away; in others, as the “ash bed” of Copper Falls, the 
trap bears little copper near the veins, but considerable when 
worked at some little distance from them. The copper in the 
vein frequently incloses completely masses of the gangue, while 
in like manner the gangue incloses the copper in other iflaces, 
and similar relations exist in the amygdules. 
After what has been said, is it possible to suppose that the 
traj^s and conglomerates could have been formed, as stated, to 
the immense thickness that they must have been before the veins 
were formed, and still retain their original heat until all was com- 
plete and the veins filled with gangue and ore? Yet Professor 
Dana’s hypothesis demands this supposition, if the writer under- 
stands it. 
Whether the percolating water was thermal or not, can only 
be determined by judging of its effects. So far as it has fallen 
under the observation of the writer, the effect of hot waters is a 
general destruction of the rock constituents, and not the changes 
that we see in the majority of old altered eruptive rocks. So 
far, then, as the writer could judge from personal observation, 
thermal waters (as set forth in his paper referred to) had acted 
in part of the district, but in other portions the water was of 
the ordinary temperature, or only slightly elevated above it, an 
opinion which Mar vine also held. 
Professor Dana, in his Manual of Geology, edition of 1862 (p. 
712), in speaking of the veins of the copper district, states that 
the metal is “ directly associated with injected dikes,” therefore he 
regards the veins as filled by injection from below. This view 
was retained in the edition of 1874 (page 731). In the edition 
of 1880 he regards the veins as contact veins which were filled 
by sublimation (vaporization) and this seems to be his present 
view. For thirty years, published evidence, that has not been 
impeached, has shown that the copper bearing traps of Lake 
Superior were not in dikes but in lava flows ; therefore it is difli 
