f 
21(5 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
to the more abundant Assuring within the surface zone of a conical volcanic moun- 
tain and partly to the parallelism of the underground isothermal surfaces with the 
surface slopes, for these surfaces would determine the depth at which the most 
active precipitation took place. 
It is believed that the vein-forming solutions ascended rapidly on a few domi¬ 
nant and very deep fissures and that they were distributed from these throughout 
the volcanic rocks, diminishing their velocity and gradually changing their compo¬ 
sition. This would help to explain the scarcity of ores in depth and the frequent 
precipitation by mingling waters at the intersection of fissures. Decrease of 
temperature and retardation of water currents are regarded as the main factors 
favoring precipitation of the tellurides. 
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