The crystals described in this paper were found one mile north-west of Sierra Blanca, Hudspeth County, Texas, where a dike of porphyritic igneous rock intrudes Cretaceous limestone. In this dike feldspar crystals occur as phenocrysts in a fine grained but holocrystalline groundmass. The region is arid and in the weathering of rocks disintegration is usually more in evidence than decomposition. In the rock mentioned above disintegration has loosened the feldspar crystals from the groundmass so that great numbers can be picked out, the crystals occurring much as fossils in a well weathered outcrop of sedimentary rock. The great abundance of the crystals, their perfection and relative freshness is thought to warrant a record of the locality.

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