PALISADE CANON EEGION. 585 



rock, containing but little hornblende. It seems, however, to be rather a 

 hornblendic than an augitic andesite. It is full of very minute crystals of 

 iron pyrites. The feldspars are generally of the same color as the ground- 

 mass, and can with difficulty be distinguished. 



The syenite body of the Cluro Hills is partly exposed in an outlying 

 peak to the west of the main crest. Between it and the andesite body is a 

 syenite-porphyry, which is practically only a porphyritic modification of the 

 main body of the Cluro Hills, but the rock is rather darker in color and 

 more fine-grained. It is a dark-green rock with small flesh-colored feldspars, 

 green hornblendes, and small quartz crystals, porphyritically imbedded 

 in a groundmass, which, under the microscope, is seen to be composed of 

 crystalline grains of feldspar, quartz, and altered hornblende. The rock 

 contains more plagioclase-feldspar than the syenite, and the crystals of 

 both feldspars are evidently fragments. The rhyolite which covers the 

 syenite on the west, at this point, has a peculiarly shaly habit, splitting into 

 thin laminae only half an inch in thickness. It is stained by iron oxide on 

 the surface, but, in the fresher fractures, shows a white, compact, felsitic 

 groundmass containing only porphyritically imbedded crystals of quartz 

 and feldspar. 



Palisade Canon Region. — In the neighborhood of PaHsade Canon, 

 the andesite core of the range has been overflowed and mostly con- 

 cealed by a flow of trachyte, which, in its turn, is covered by extensive 

 flows of rhyolite, which mask the greater portion of the range north of 

 the river. Most of the cliffs which border the canon west of Palisade 

 Station are composed of a dark-gray sanidin-trachyte. This rock contains 

 but very little plagioclase or macroscopical biotite. Under the microscope, 

 the groundmass is seen to contain a large quantity of very fine laminae 

 of mica, together with decomposed hornblendes, and some apatite, but 

 no augite. It has also a good deal of magnetic iron, which is frequently 

 decomposed into dendritic fibres of ferric oxide. Apparently inclosed 

 in this trachyte, on the south bank of the river, at the mouth of a little 

 side-canon, is a hill a few hundred feet in height, containing a large 

 mass of iron-ore, remarkably fine-grained, and having a thoroughly con- 



