12 DESCEIPTIVE GEOLOGY. 



the zones and bands of minerals seem but little disturbed or twisted in com- 

 parison with the beds found to the south in the Colorado Range. 



At Dale Creek, near the railroad-bridge, there occurs a granite mass, 

 which, from its peculiar habit and contrast with the ordinary granites of the 

 range, deserves special mention. It forms the canon-walls of Dale Creek, 

 which, at this point, rise abruptly for 125 feet above the stream-bed. It 

 is a very coarse-grained, but compact rock, with an intensely deep red 

 color. The component minerals are chiefly broad tabular crystals of or- 

 thoclase, with white and gray vitreous quartz, which seems to occupy the 

 interstices between the feldspars. The mica is of a dull black color, similar 

 to that observed in the granite from Granite Cailon, which has been referred 

 to lepidomelane. Under the microscope, triclinic feldspars have been de- 

 tected, and the quartz shown to contain but few liquid-inclusions. This 

 granite develops no stnictural lines or divisional planes, and the minerals 

 are brought together without any observable order in their association 

 with each other. In contrast with the prevailing granite of the central nu- 

 cleus, this one withstands the action of the weather remarkably well, and 

 has been used to some extent for building purposes. The railroad-company 

 quarried it in massive blocks for the piers of their bridge over Dale Creek. 

 A similar granite, although somewhat finer-grained, occurs in the Adiron- 

 dacks, near Boonville, Lewis County, New York. 



At Iron Mountain, just north of Chugwater Creek, the granite is of 

 interest, from its association with a large body of ilmenite. It forms the 

 walls of the intercalated iron bed, while frequently large masses occur pro- 

 truding into the iron, and almost completely surrounded by the heavy min- 

 eral. It is essentially an orthoclase-granite, with a few triclinic feldspars. 

 The quartz occurs in small grains, well disseminated through the rock. 

 Biotite in brilliant dark plates is much more abundant than is usually the 

 case in the fine-grained granites of the Laramie Hills. It is a true granite, 

 without any distinct evidence of structural lines. 



