DAT ALLAH EANGE. G77 



but few Isolated points 1,000 feet above the Quaternary gravels, which 

 skirt the base. Both to the north and south it is overlaid unconformably 

 by the sedimentary beds referred to the Star Peak Triassic. But little 

 opportunity was afforded for the proper examination of this body; it may be 

 said, however, in its general habit and modes of erosion to resemble the 

 mass of granite upon the opposite side of Ragan's Valley, if, indeed, thev 

 do not form a continuous body broken on the surface by a thin deposit of 

 fine Quaternary material. It is perhaps a little more compact, and of a 

 deeper red color, owing to the prevailing dark tints of the orthoclase-feld- 

 spars, and shows distinct structural lines of bedding, with a dip toward the 

 west. 



At the southern end of this granite, and just north of Gold Run Creek, 

 occurs a dike penetrating the older formation. It is between 20 and 30 

 feet in width, stands nearly vertical, with a stiike approximately north and 

 south, and in its habit resembles basaltic outbursts, which are found pro- 

 truding through the granite in the same region. This rock has, however, 

 a somewhat singular composition, differing mineralogically from all other 

 eruptive rocks in our collection. It is very dense, with a high specific 

 gravity, and develops but little tendency to decomposition. The crypto- 

 crystalline groundmass is so fine that to the unaided eye it reveals scarcely 

 anything of the interior structure, but scattered through it, porphyritically 

 enclosed, are broad crystals of beautiful dark-green fibrous hornblende, with 

 occasional segregated patches of minute mica flakes. The microscope shows 

 that the groundmass is made up almost exclusively of fine quartz and horn- 

 blende, the latter frequently appearing as if distributed through a base 

 composed of the former mineral. The presence of hornblende in so large 

 proportions renders it impossible to relate the rock to any member of the 

 basaltic group, while, on the other hand, the almost complete absence of 

 feldspars makes its reference to any variety of eruptive rock equally 

 insecure. 



The basalts penetrating the granite are mostly small outbursts, which 

 form narrow dikes or irregular-shaped bodies capping the older formation. 

 Like the granite, the inclination of the basaltic flows is to the westward, 

 A specimen in the collection from here shows a tough dense rock, breaking 



