86 ALASKAN MINERAL RESOURCES IN 1904. [bull. 259. 
occurrence of so large a majority of the veins in parallel position with 
it, and it may be supposed that this control has prevented the forma- 
tion of a large number of fissures in various directions, which would 
have resulted in the case of homogenous or massive rocks deformed 
under their own weight. 
Having been subjected to the same pressures as those which frac- 
tured the other rocks of the region, it is only natural that the Tread- 
well dikes should be broken along lines parallel with the general 
Assuring, and one of the two sets of veinlets occurring in the ore 
bodies practically coincides with the structure of the inclosing slates. 
The other set, which stands at right angles to the first, is not nearly 
so well developed in the country slates, probably because these } 7 ielded 
by bending, since they are very flexible when compared with the 
brittle rock of the dikes. 
SOURCE OF THE VEIN-FORMING WATERS. 
The formation of the Treadwell ores is assigned to the same general 
cause as the other veins of the region. Both are attributed to circu- 
lating waters moving through channels opened by a general fracturing 
of the rocks. 
From the nature of the metasomatic changes which the waters have 
effected, and also from the large amounts of carbon dioxide which 
they evidently contained, it may be assumed that they were ascend- 
ing. a That they were hot may also be safely predicated, because the 
erosional history of the region indicates that the veins now exposed 
must have been deposited at great depths, certainly not less than from 
6,000 to 10,000 feet below the former surface and possibly very much 
deeper. The occurrence of tourmaline in some of the veins of Gold 
Creek, and the occasional presence of fluorite elsewhere, suggests a 
connection with igneous emanations, for these minerals are character! 
istic of pneumatolytic action, as exhibited in the case of tin deposits 
and in various instances of contact metamorphism. The presence of 
these minerals can not be pushed to the value of evidence because 
neither of them have been universal!} 7 observed in the district, but,, 
even for those who hold the theory that the final source of mineralizing 
water is mainly meteoric, their occurrence may be admitted as prob- 
ably significant of at least accessory contributions to the vein-forming 
solutions from igneous sources. 
It is concluded that known facts do not lead to a recognition of thd 
actual source of the solutions which have formed the mineral deposits, 
and any present idea of their origin must rest largely on speculation. 
I am inclined to believe that the very wide occurrence throughout 
southeastern Alaska of intrusions related to, and of practically iden- 
aLindgren, W., Gold-quartz veins of Grass Valley district, California: Seventeenth Ann. Rept. 
U. S. Geol. Survey, pt. 2, p. 173. 
