592 DESOEIPTIVB GEOLOGY. 



Merychippus mirahilis,^ another equine animal, represented by an upper 

 molar tooth; and 



CosoryXy represented by a peculiar furcate fragment of a horn-core, 

 supposed to belong to an extinct family of antelopes. 



The ridge to the west of Bone Valley is made up of quartzites and 

 slates, striking a little north of east, and dipping about 25° to the eastward, 

 on whose flanks along the southern portion are some conformable limestone 

 beds. No fossils were obtained from any of the beds, but from their asso- 

 ciation and position they have been assigned respectively to the Weber 

 Quartzite and Upper Coal-Measure groups. 



Egyptian and Osino Canons.— The North Fork of the Humboldt, which 

 here forms a considerable stream, takes its rise in the valley next west of 

 Bone Valley, and, after leaving the open region of these two valleys, flows 

 southward for 6 to 8 miles through a narrow canon-like gorge called Egyp- 

 tian Canon. In this canon is exposed a peculiar rock, which, from its posi- 

 tion, is apparently older than the surrounding rhyolites. It has been colored 

 on the map as an andesite, although Professor Zirkel has, from a study of 

 the microscopical sections, classed it among the basalts. In physical habit, 

 it resembles the andesites. Its manner of weathering is rather peculiar, 

 showing a rudely columnar structure, in which the columns are of cylindrical 

 rather than prismatic shapes, and have a tendency \o split into curved lam- 

 inae or sherds, at right angles to the axis of the cylinder. This peculiar 

 weathering produces singularly picturesque architectural forms on the clifi"s 

 of the rock, which frequently show resemblances to ruined columns and 

 remains of ancient temples. 



The darker, more compact variety of the rock which is found at the 

 lower end of the canon is almost black, and shows only a few small crystals of 

 feldspar in a semi- vitreous groundmass. Under the microscope, the ground- 

 mass is seen to be made up of a mixture of fine microlites and grains of 

 plagioclase, and augite. It contains, however, no olivine. Another variety, 

 which shows the prevaiHng character of the rock, has a dark brownish- 

 gray groundmass, in which are imbedded large crystals, often half an inch 

 in diameter, of sanidin, rounded, cracked quartz, and also microscopical 

 iLeidy, Extinct Mammaliau Fauna, 1869. ^ibij,^ 172. 



