424 GEOLOGY AND MINING INDUSTRY OF LBADVILLE. 



material, which occasionally passes into limestone, the roof being White 

 Porphyry. The left-hand or west fork in the first half of its course is cut 

 in White Porphyry and then passes into a decomposed, light-colored, and 

 iron-stained limestone, which rises to the west. The drift, after a rise of 15 

 feet over a ridge of dark hard limestone, passes into soft clayey material, and 

 then bending to the northward passes through two or three feet of quartz- 

 ite into a body of Gray or Mottled Porphyry, in which it stops. This is 

 the only point in which the Gray Porphyry has been discovered in this 

 mine. No definite idea, therefore, can be formed as to the shape or origin of 

 the body. It may be interesting to note in this connection, however, that 

 farther in the hill, as shown by the developments of the Modoc shaft, there 

 are several bodies of this Mottled Porphyry intercalated between the differ- 

 ent beds of limestone. From this level, immediately adjoining the Main 

 incline, an incline drift, following the contact, has been run westward to a 

 point immediately under the fifth level. It is now mostly filled up, and is 

 mainly interesting as proving the existence of the deep trough shown in the 

 section. 



From the eighth to the ninth level, a distance of over one hundred and 

 twenty feet, no pay ore is found ; but, as has already been mentioned, most 

 interesting proof is, afforded of the fact that the ore bodies are simply 

 replacements of the limestone. The replaced material is largely a black, 

 clayey matter, more or less iron-stained and in some cases passing into a 

 red plastic clay, which would seem to have infiltrated into the mass from 

 the porphyry above, while the limestone immediately adjoining this is itself 

 more or less discolored by black oxide of manganese. A short distance 

 below the intersection of the ninth level, which is in solid blue limestone, 

 the limestone, with its contact seam of Chinese talc, dips steeply down to 

 the eastward and the incline passes into porphyry. Just at the point where 

 the limestone bends downward, a small ore body was discovered immedi- 

 ately over the roof of the incline. 



Little Giant. — The Workings of the Little Giant mine are practically an 

 extension of those of the Carbonate along the continuation of the main 

 ore sheet, where it has its steep dip to the eastward between the fourth and 

 seventh levels. It is opened by a shaft 234 feet deep and is also connected 



