THE ORIGIN OF THE WOLFRAM XSD CASS1TERITE ORES. 333 



the Tavoy district that this aqueous portion did not segregate 

 below the granite as it is generally supposed to do, but that it appears 

 to have been held to a great extent in a band of granite a few hundred 

 feet thick at the upper margin at the stage when it was only 

 partially solidified, in much the same way that water is held in a 

 sponge. The only explanation of this is said to be that a steady 

 influx of meteoric water has taken place and has been absorbed 

 locally at points on the periphery. The occurrence of aplite dykes, 

 pegmatite veins and patches of granite on the upper margins of 

 batholiths, all carrying tin-ore and wolfram, but only in the vicinity 

 of mineralised quartz veins, and the fact that tin and tungsten 

 minerals usually occur within small circumscribed areas in narrow, 

 numerous and parallel veins, is believed to be explicable only on 

 the hypothesis that meteoric water reached the granitic portion of 

 the magma in varying quantity, and at definite points during the 

 differentiation period. 



The pneumatolytic theory is regarded as overworked, but fashion- 

 able because those who follow it have not troubled to doubt or to 

 prove its applicability. It is argued that there is good reason for 

 believing the association of tourmaline, fluorides, etc., with cassiterite, 

 presumably anywhere in the world, to be fortuitous and not genetic, 

 and that there can hardly be two modes of origin of cassiterite, one 

 for Tavoy and another elsewhere. The absence of intense local 

 metamorphism of the country rock near veins, leads Dr. Campbell 

 to the belief that the temperature of ore deposition in the veins of 

 sedimentary rocks was below that at which pneumatolysis would 

 be possible. 



To most of these opinions we demur. 



W. R. Jones, 1919. 1 — Dr. Jones has replied to Dr. Morrow 

 Campbell's first paper. He reiterates his views that both mineraliz- 

 ing gases and mineralizing solutions played their parts in ore deposi- 

 tion and that both were of deep-seated origin. The former have 

 been the chief agents and he sees no point in separating the one from 

 the other on paper, when in nature they are found in many cases to 

 have functioned together. He also mentions recent analyses of the 

 water from a hot spring in Malacca, which have failed to confirm St. 

 Meunier's analysis that it deposited a siliceous sinter containing 

 0-5 per cent, Sn0 2 . This analysis had been quoted by Dr. Campbell. 



1 W. R. Jones Second Series of leoture* delivered at Tavoy. (In th© press.) 



