BEEECE IRON MINE. 499 



and explained in Part I, Chapter V. On the other hand, it is the Weber 

 Shales that are ordinarily found between the Gra}^ and White Porphvry 

 sheets, and in the Theresa (K-57) shaft, a short distance to the northeast, 

 hij,''hly pyritiferous shales were found in this hoi'izon at a depth of 325 feet. 

 Breece Iron mine. — In a similar positiou occurs the deposit of the Breece 

 Iron mine, situated on a spur of Breece Hill, overlooking Adelaide Park. 

 This remarkable deposit of iron ore is found at the surface in two distinct 

 bodies, shown in open cuts, the one a short distance above the other. The 

 lower body has a maximum thickness of 20 to 25 feet and rests on White 

 Porphyry, with a mottled porphyry on the hanging wall. The upper body 

 is not so thick and is overlaid by the main sheet of Gray Porphyry; both 

 dip eastward, and the shaft (K-39) higher up the hill has been sunk through 

 30 feet of iron without reaching the bottom of the body, from which it may 

 be supposed that the two bodies have here come together. The Gray Por- 

 ph3n-y has either the characteristic large crystals of orthoclase or the cavities 

 which they once filled. The intermediate porphyry is, however, of finer 

 grain, of a pinkish color, and is full of minute cavities having the form of 

 crystals of pyrite. This may possibly represent a tongue of Pj-ritiferous 

 Porphja-y extending between the two iron bodies. The lower (K-36) shaft 

 has been sunk 350 feet in the underlying White Porphyry, which, near the 

 iron body, is also impregnated with pyrite. The iron bodies are rather 

 irregular in shape and send offshoots or stringers into the surrounding rocks. 

 The ore is, however, massive and compact and remarkably free from earthy 

 gangue. It has been largely used as a flux in the smelting works, being 

 supposed to carry several ounces of silver to the ton, and has also been 

 used by the Colorado Coal and Iron Company in the manufacture of 

 Bessemer steel. It is a very pure hematite, with a certain admixture of 

 magnetite which seems to occur mainly near the outcrop. It carries about 

 GG per cent, of metallic iron. The complete analysis of an average specimen, 

 b}- Mr. Guyard, will be found in Appendix C. Undecomposed pyrites are 

 found in the ore from the upper shaft. It seems probable that this body, 

 like the iron bodies in tlie various silver mines, is the result of the 

 oxidation of pyrites, which were concentrated at the junction of the three 

 bodies of porphyry. It difi'ers in being anhydrous, while all the others are 



