tANSOME.] THE STOCKS OR MASSES. 107 
>f the small Zuiii ore body no such solvent action was detected. The 
oregoing explanation is essentially that proposed by Emmons 1 in 
888, when he pointed out the similarity existing between the Yankee 
Jirl mine and the Bull Domingo and Bassick mines in the Silver Cliff 
listrict, Colorado. As described by L. R. Grabill, 2 the Bassick ore 
>ody fills an irregular opening nearly elliptical in plan and varying 
rom 20 to 30 feet on the shorter diameter to nearly 100 feet on the 
onger. It extends vertically downward for nearly 800 feet. No 
rails have been found, and there is no distinct boundary between ore 
lid country rock. Emmons 3 concluded that the ore body was due to 
uinaiolic action in the throat of a volcano after all explosive action 
unl ceased. He remarks, however: 
It would appear * * * that it was the intersection of certain fracture 
'lanes that determined the course of the ore-bearing channel, and that the ore 
>ody is not necessarily the center of the volcanic vent, but that, as a second ore 
hininey has already been discovered on one side of the first, it is by no means 
tnpossible that other chimneys or ore shoots may exist in the body of the agglom- 
rate, which might be discovered by judicious and systematic exploration in the 
irection of the principal fracture planes. 
In the Bassick mine the ore was deposited in the agglomerate, 
eplacing the fine interstitial tuff and partly replacing the larger 
r olcanic fragments. 4 It will be recalled that a somewhat similar 
eplacement of the San Juan breccia by ore was noted by Mr. 
Cmmons in the Yankee Girl mine (p. 216). In the Bull Domingo mine 
'the ore occupies a nearly vertical chimney-like channel in a con- 
.lomerate or breccia mass, and the minerals are deposited in concen- 
ric scales around the bowlders or rock fragments." 5 This ore 
hannel "was primarily formed b}^ a complicated intersection of a 
lumber of fracture planes which produced a zone of broken country 
ock, in which the included fragments maj 7 have been somewhat 
ounded by attrition, but whose final rounding was more likely com- 
peted by the solvent action of percolating solutions." 6 
It is evident from the descriptions given of the Red Mountain 
tocks that the term "chimney" applied to them is somewhat mis- 
eading. They are nol simple vertical pipes of ore extending from the 
urface to indefinite depths, but are separate bodies of irregular, 
enticular, or spindle-shaped form, often completely inclosed by 
ountry rock, but linked with neighboring stocks by fissures which 
re often small and which carry little or no ore. There is no evi- 
lence whatever to indicate that they occupy the necks of former 
'olcanoes. Although they occur in volcanic breccia, it is the 
1 Structural relations of ore deposits: Trans. Am. Inst. Min. Eng., Vol. XVI, 1888, pp. 833-834. 
2 On the peculiar features of the Bassick mine: Trans. Am. Inst. Min. Eng., Vol. XI, 1882, p. 110. 
3 The mines of Custer County, Colo.: Seventeenth Ann. Rept. U. S. Geol. Survey, Pt. II, 
■J90, p. 436. 
4 S. F. Emmons, loc. cit., p. 438. 
5 Emmons, loc. cit., p. 445. 
6 Emmons, loc. cit., p. 446 
