CONCENTRIC ARRANGEMENT OF MFNERALS. 71 



From this brief notice of the components of the granite it is seen to be 

 exceedingly coarse, feldspathic, and crystalline, and it would probably be 

 classed by Nauman and Von Cotta as approaching the variety Pegmatite. 

 In the southern end of the Hills, however, on French Creek and the 

 headwaters of Amphibious, a fine-grained variety was found which has 

 more nearly the typical character of granite. In places it has much the 

 appearance of Scotch granite, though considerably coarser in texture, and 

 in nearly every hand specimen that may be selected crystals of tourmaline 

 can be found, but these are neither so large nor so finely crystallized as 

 those in the coarser rock. 



In one of the smaller granite deposits in Custer Park a particular 

 arrangement of the minerals was observed, which, though interesting, is 

 quite exceptional. The tourmaline, mica, and quartz have a roughly con- 

 centric disposition within the general matrix of feldspar. On the exterior 

 of each aggregation the tourmaline preponderates, with a sprinkling of 

 quartz. In an intermediate layer the tourmaline is less abundant, and asso- 

 ciated with quartz are quantities of mica in crystal tablets, while a large 

 mass of clear, highly crystalline quartz constitutes the nucleus. 



In the great peaks and masses of the central nucleus there seems to be 

 an arrangement in a north and south direction, i. e., their greater diameters 

 have that trend. There are many cross ridges, it is true, but they appear 

 to be due rather to an accidental arrangement of the deep eroded valleys 

 that wander through the granite area than to any primary arrangement of 

 the granite itself. No distinct marks of stratification were observed even 

 in a large way. The main peaks are of massive granite, fissured and 

 cracked, weathered and worn in every direction, but they are longer in a 

 northeast and southwest direction and comparatively narrow crosswise, 

 forming in many instances crests or ridges. South and southwest of Har- 

 ney are some excellent examples of what might be termed weathering 

 planes, in which granite pinnacles or slabs are weathered out and stand 

 100 or 200 feet above the mass of the range. These planes have the same 

 general northwest or north-northwest trend observed in the whole struct- 

 ure of the granite area. They divide some of the crests into serried pin- 



