ANTELOPE HILLS. 485 



to be distinctly crystalline, and made up of quartz, feldspars, mica, and 

 hornblende, the latter often fibrous. Apatite and magnetite occur, the latter 

 in very well-defined crystals. In the more granitoid varieties are some 

 striated plagioclases and microscopical titanite. The quartz contains included 

 portions of the groundmass, and both empty cavities and liquid-inclusions, 

 among which are some with carbonic acid, but no glass-inclusions. In 

 one of the more porphyritical varieties is seen a tendency toward felsitic 

 porphyry in the presence of a few sphasrulites. It contains well-defined 

 titanites, and its hornblendes are not fibrous. 



The numerous mineral veins which occur in these rocks have a general 

 northerly strike, with that of the inclosing rock. They had not been opened 

 at the time of our visit, but showed considerable green carbonate and red 

 oxide of copper in the outcrops. The rock which forms the core of the main 

 ridge, though having something of a generic resemblance to the porphyries, 

 has been colored rather as a granite than a porphyry. It is a whitish, 

 somewhat decomposed-looking rock, made up of quartz, feldspar, mica, and 

 hornblende, in which the prominence of the latter and of the larger feld- 

 spars, in the distinctly macro- crystalline white mass of the rock, has some- 

 what of a porphyritic appearance. 



The low hills to the south known as the Antelope Hills are made up 

 of flows of various rhyolites. Of these, there is found directly adjoining 

 the Marble Hill on the south a brick-red porphyritic rhyolite, somewhat 

 resembling that of Spring Canon. It contains white opaque feldspar, 

 quartz, mica, and hornblende in a red compact felsitic matrix. The quartzes 

 are sometimes associated together in lenticular bodies through the mass, 

 and are found in very perfect crystals lining small druse-like cavities. 



On the main ridge south of Leech Springs, so named from the abund- 

 ance of these animals in its waters, is a reddish rhyolite containing large 

 hornblendes, but no macroscopical quartz or mica, in a groundmass which 

 shows ver}' distinctly the characteristic banded structure of these rocks. 

 Under the microscope, these bands are shown to be made up of alternations 

 of sphserulitic fibrous material, with bands of an imperfectly granular nature, 

 without tendency to fibration. The rock is seen to contain characteristic con- 



