Page 15 - The Mines of Kingston, New Mexico

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in the district being plainly traceable for miles. In some places the porphyry fails to intrude itself clear through the limestone to the surface, but after rising to a certain plane, has spread out and is now found in the condition of an interstratification in the sedimentary rocks. This is accounted for on the hypothesis that only at the weaker places of the original formation, was the intrusive force suf- ficient to cause the limestone to break and allow the molten lava access to .the top. Hence it is that at points along their course the porphyry dykes are apparently lost, and also that the lime sometimes
appears overlying the porphyry, as shown by development shafts and erosion in the adjacent gulches. Argyllaceous limestone is also
found in portions of the district, and always overlying the dolomite.
It does not, however, appear to have exercised any influence in the
deposition of the contents of the mineral waters in their How, al-
though ore is sometimes found between it and the underlying strata.
It is to the presence of these dykes, and the numerous Quits, slides
and fractures in the limestone, caused by them, that the Percha dis-
trict owes its mineral wealth. The quartz ledges which mark the
surface of the country are also noted for their metalliferous value.
Theypresentnospecialfeaturesdeservingofmention. Theirori-
gin, together with the deposition of thw metallic compounds held by
them, being undoubtedly contemporaneous with the formation of the ore belts and veins of the porphyritic ami limestone rocks. Nat-
urally in such a formation the experienced prospector looks for more than one distinct type of mines. In this respect the Percha
country is remarkable, not only in presenting several well defined species, but also in showing the characteristics of each kind to a marked degree.. Thus it is that there are contact-fissures, limestone deposits, quartz leads and fissures in trachyte. The first are those whose main ore bodies are or will be found at the point. of juncture between either edge of the dykes and the limestone through which they cut. The second are those in which the ore is found interbed-
ed with and lying conformably to the general plane of the lime stratification. In both these classes of mines, and notably in the
first mentioned, the ore is found frequently branching off from the main shoots and forming pockets irregularly distributed throughout
the limestone, but occurring principally along the joint planes of the fracturesandfaultswithwhichthelatterrockabounds. Wheretwo