634 DESCRIPTIVE GEOLOGY. 



The analysis was made by Mr. R. W. Woodward, who reported the 

 following composition: 



Silica 10.38 



Lime 48.98 



Magnesia 0.94 



Ferric oxide 0.44 



Carbonic acid 39.02 



Sulphmic acid 0.24 



100.00 

 Combining acids with bases, we have: 



Carbonate of lime 87.18 



Sulphate of lime 0.40 



Carbonate of magnesia 1 1.26 



Excess of magnesia 0.34 



Ferric oxide 0.44 



Silica 10.38 



100.00 



The rhyolite through which the spring reaches the surface is not only 

 a very beautiful rock, but may be considered as typical of the region. It 

 shows a very variegated coloring, from light-gray to reddish-gray, purple, 

 and lilac. It has a fine microfelsitic groundmass, with a tendency to pass 

 into a lithoidal texture. In a thin section under the microscope, the ground- 

 mass has a characteristic rhyolitic habit. The feldspars are mostly small 

 and decomposed. The quartz is both abundant and large, and scattered in 

 a most irregular manner through the rock. 



The Upper Quaternary, through a great part of Eeese River Valley, 

 would appear to be extremely thin, and to give place rapidly to the Lower 

 Quaternary, which consists of exceedingly fine argillaceous and arenaceous 

 beds, forming almost an impalpable powder. In most years of moderate 

 water-supply, the river, after leaving the canon, sinks in the broad basin east 

 of the Fish Creek Mountains, the drainage-channels spreading out over a 



