470 W. Cross — Alunite and Diaspore 



and is made of a hard, rough, porous rock — a decomposition 

 product, varying locally in character, but exhibiting in few. 

 places any trace of the original rock structure. The crest rep- 

 resents the extreme alteration. Along the base of the summit 

 cliffs is a plain contact between spherulitic rhyolite and ande- 

 site, and at either end of the crest the harder rock gives way 

 to modifications showing spherulitic structure, and in one 

 direction the body is continued for some distance as a distinct 

 rhyolite dike, cutting through andesite. 



The rock composing the rough outcrops of the summit ridge 

 is often much like the alunite-bearing mass of Democrat hill, 

 and is in places identical with it, but it is much less uniform in 

 character. Certain masses are composed of bluish cellular 

 quartz, and barite appears developed in great irregular tablets 

 in a few spots. On the whole, alunite is not developed in so 

 large grains as in Democrat hill, and through the numerous 

 minute quartz grains included in it the cleavage faces are less 

 distinct, the result being a dull whitish or slightly yellowish 

 rock of dense texture save for small irregular pores containing 

 kaolin or yellowish ochre. A specimen of such rock from the 

 eastern end of the crest, whose composition cannot be made 

 out macroscopically, but which exhibits a large amount of 

 alunite in thin section, was analyzed by Mr. Eakins and found 

 to contain : 







Molec. ratio. 





Si0 



-._ 69-67 







A1 2 3 ---- 



... 13-72 



•134 



4*8 



CaO 



0-07 







M^O 



tr. 







K 



Na,0 ._.. 



2-44) 

 0-34 f 



•032 



1-1 



S0 3 



9-27 



•114 



4-0 



H 2 (K____ 



4-73 



•263 



9-4 



100-24 



The alkalies present are but very slightly in excess of the 

 amount required to go with the sulphuric acid to form alunite, 

 while there is a considerable residue of alumina and water 

 belonging to kaolin, the presence of which is shown by the 

 microscope. The percentage of S0 3 found corresponds to 

 23*96 per cent of alunite. 



Toward the west end of the crest-ridge, and also near the 

 middle, there is much of a rough, finely cellular rock consisting 

 almost exclusively of bluish quartz and a transparent colorless 

 mineral in irregular grains, noticeable on account of the bright 

 luster on a very perfect cleavage plane. This mineral was at 

 first supposed to be alunite in an unusually pure state. With 



