﻿202 Caimdian Record of Sciaiec. 



The auriferous deposits, which occur in the intrusive granites, 

 appear under conditions differing from the true lodes in sedimentary 

 rocks, as the intrusive granitoid rock forms dykes, which fill fissures in 

 the older true granites, and also cut through the sedimentary slates. 

 It bears evidence of intrusion in a state of fusion, or at least in plastic 

 condition, and has subsequently crystallised, after whicli there has 

 been shrinkage, causing cavities, as the sides of the dyke were held in 

 position by the enclosing rock. The vertical shrinkage being greater 

 than tlie horizontal, the cavities were nearer the horizontal than 

 the vertical, and, being afterwards filled with ore, formed what 

 are called floors, one characteristic of which is the tendency to 

 lenticular form, or a central maximum thickness with thinner edges. 



E. T. Chambers. 



