332 QUICKSILVEK DEPOSITS OF THE PACIFIC SLOPE. 



deposits also have long baen known to be of extraordinav}- interest, because 

 thov contain metallic compounds, including cinnabar and gold. So much 

 cinnabar is found here in areas still emitting steam and sulphur gases that 

 mining operations were undertaken some years since aud a furnace was run 

 for a time on the ore. That quicksilver was produced is certain, though 

 I was unable to ascertain how man\- flasks. A considerable amount of ore 

 is in sight, aud there is no apparent reason to doubt that were the price of 

 the metal to rise to a dollar a pound the deposit might be worked at some 

 profit. 



Here, if anywhere, the question of the mode of genesis of cinnabar 

 deposits can be settled, and the study of the locality was undertaken on 

 that account. The results of this study and of laboratory experiments 

 suggested by it appear in this and succeeding chapters. 



Granite — The litliological character of the nuissive rocks of Steamboat 

 has been described in Chapter IV, and the details do not require repetition 

 here excepting in reference to the distribution of the rocks and their rela- 

 tions to field habit. The granite, wdiich is exposed to a large extent, mani- 

 festly underlies the whole region. In external appearance it is thoroughly 

 typical, and no geologist would doubt for a moment how to classify it. It 

 is unstratified, much fissured, weathers irregularly, and sometimes crumbles 

 to a coarse gravel, as granites often do. Some of it is coarse, and it dis- 

 pla3-s considerable irregidarities in texture and mineralogical composition, 

 as if it had never been thoroughly fluid. Plagioclase is occasionally visible 

 with the naked eye, but the predominant feldspar seems to be orthoclase. 

 Under the microscope this granite appears less topical, inasmuch as the 

 quantity of triclinic feldspar seems in the slides unusually lai-ge, and one 

 might well doubt whether to class some of the rock as orthoclastic or pla- 

 gioclastic. This is one of the cases in which the appearance is less truthful 

 under the microscope than to the unaided vision, and this is doubtless due 

 to the fact that the plagioclase is recognized by positive characters between 

 crossed nicols, while the presence of orthoclase is evinced chiefly by the 

 absence of polysynthetic structure. Separation by specific gravity shows 

 that the more plagioclastic specimens of the rock contain about as nuich 

 orthoclase as plagioclase. The granite of Steamboat Springs is substan- 



