308 GEOLOGY OF THE EUKEKA DISTRICT. 



the time the luiiin ridge was uplifted. Other faults indicate lateral thrust, but 

 they are less eifective than the former and may be of later origin, due to sub- 

 terranean forces connected with the period of volcanic energy. Accom- 

 panying these are innumerable small fissures, seams, crevices, chambers 

 and channels of varied shapes and sizes. Many of these owe their origin 

 simply to the dynamic effects of upheaval. Others are best explained on 

 the theory of surface waters percolating downward along lines of least 

 resistance, widening fissures and enlarging caAdties. If these waters w^ere 

 charged with carbonic acid, chambers and irregular shaped galleries and 

 drainage channels must necessarily have been dissolved out of the limestone. 

 A study of these channels and their intricate connections tends to the belief 

 in the theory of preexisting caves and underground water coui'ses before 

 the introduction of ore. 



Filling of Fissures.— The comiug ill of the volcanic period would be quite 

 likely to disturb and dislocate any previous system of subterranean di'ain- 

 ao-e, in some places complete!}' closing and in others opening new channels 

 l)y the formation of fresh cracks and crevices. Subsequent to the peneti-a- 

 ting of the main fissure by rhyolite came the filling of minor fissures and 

 other openings in the limestone by the ascending mineral solutions and 

 o-aseous currents. Wherever the narrow fissures admitted of it these open- 

 ings and chambers were more or less filled with mineral matter precipitated 

 from solution, the passage ways in many instances being left nearly barren 

 or onlv carrying stringers and slight indications of earthy, ocherous 

 material probably deposited liefore the dying out»of the active mineral 

 currents. In some instances the narrow connecting channels between the 

 larger openings are richer in mineral matter than the chambers themselves. 

 It would be useless to s})eculate on the reasons Avhy certain fissures and 

 chambers carried ores and others were left baiTen. The freaks of deposi- 

 tion from ascending currents — in some places rapid, in others slow — and the 

 var^nng conditions of temperature and pressure brought about by the vary- 

 ing intensity of solfatarie action would produce endless differences in the 

 mode of occurrence. Channels which at one time presented conditions 

 most favorable for deposition might at a later period become entirely cut 

 off from ascending currents. Anyone Avho has observed carefully the 



