136 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
important lodes of the Silverton quadrangle no erustification can be 
detected. The fissures are filled by coarsely crystalline allotriomor- 
phie aggregates of ore and gangue (massive structure), and there is 
no evidence to show that such a structure could result from successive 
deposition upon the walls of the fissure until the whole was finally 
filled. On the contrary, crystallization has proceeded simultaneously 
from many points within the solution. Quartz, galena, pyrite, spha- 
lerite, chalcopyrite, and other minerals have formed practically con- 
temporaneously about local centers of crystallization scattered irregu- 
larly through the solidifying mass. It is difficult to conceive all the 
details of a process which results in the formation from aqueous solu- 
tion of an irregular allotriomorphic aggregate of minerals differing so 
widely in specific gravity. But reasoning from analogy with similar 
structures met with in petrology and in the arts, it is fair to assume 
that this structure in veins is the result of the undisturbed crystalli- 
zation of a nearly motionless saturated solution. In other words, it 
was the crystallization of a reservoir so large, in comparison with the 
current or currents which circulated through it, as to have been itself 
free from megascopic motion. The conditions which induced crys- 
tallization were present throughout the mass of material which filled 
the fissure, and solidification, instead of proceeding gradually from 
the walls inward, took plaee almost simultaneously, although not nec- 
essarily with rapidity, throughout the mass. Obviously this massive 
structure and erustification may be present in the same vein. In such 
cases deposition appears to have begun by erustification next the 
walls, passing at a later stage into the more general mode of crystal- 
lization indicated by what has been described as massive structure. 
Attention has been strongly drawn of late, through the writings of 
De Launay, 1 Van Hise, 2 Weed, 3 and Emmons, 4 to the important part 
played by secondary sulphide enrichment in the formation of many 
ore bodies, particularly those carrying copper and silver. As a prob- 
able example of such an enriched deposit, Mr. Emmons 5 has cited the 
Yankee Girl ore body. Unfortunately, at the time Mr. Emmons vis- 
ited the mine, in 1888, but little attention had been given to the sub- 
ject of secondary sulphide enrichment, while at the present day the 
state of the workings is such as to render impossible the verification 
by direct observation of this application of the theory. However, 
there are many facts which point strongly toward secondary* enrich- 
ment as the true mode in which the rich ore bodies, not only of the 
Y'ankee Girl, but of the Guston, Silver Bell, and other mines, were 
formed. To have the important fac\3S fresh in mind, it will be well to 
1 Contribution a Tetude des gites metalliferes: Ann. des Mines, Vol. XII, 1897, pp. 119-228. 
2 Some principles controlling deposition of ores: Trans. Am. Inst. Min. Eng., Vol. XXX, 1900. 
pp. 27-177. 
3 Enrichment of mineral veins by later metallic sulphides: Bull. Geol. Soc. Am., Vol. XI, 1900, 
pp. 179-206. 
4 The secondary enrichment of ore deposits: Trans. Am. Inst. Min. Eng., Vol. XXX, 1900, pp. 
177-217. 
5 Loc. cit., p. 19. 
