Correspondence — J. W. Gregory. 139 



that Fouque & Levy do not directly challenge them. It will, 

 however, be noticed that the papers of Dr. Sorby and Professor 

 Hartley, published as they are in the records of Societies such as 

 the Eoyal, Chemical, Microscopical, and Mineralogical, and in the 

 Reports of the British Association (and published, moreover, quite 

 independently, and for dijfferent objects of research), might very well 

 not have all come under the notice of MM. Daubree, Fouque, and 

 Levy ; and that indeed seems to have been the case. 



Speaking for myself, I certainly should not have seen most of the 

 above papers had not the authors most generously sent me reprints. 



1 am certainly in a great difficulty. One of the minerals relied 

 on by the Geological Survey to prove pneumatolytic action at 

 temperatures above the critical temperature of water is topaz. But, 

 in Professor Hartley's paper on Fluid Cavities to the Chemical 

 Society in 1877, one section is entitled " On the Probable Temperature 

 incident to the formation of Topaz," and one conclusion arrived at is 

 that topaz sometimes crystallises under and sometimes over the C.T. 

 of water. 



The petrologists dismiss all the evidence relied on by the chemists 

 for ascertaining the temperatures of rock-formation. But there is this 

 fact to be borne in mind, that while the chemists have minutely 

 studied separate minerals, the petrologists have taken a wider view 

 of rocks and magmas. 



The following example will serve to show how widely eminent 

 petrologists and chemists differ as to probable temperatures. Professor 

 Hartley, in discussing the formation of negative cavities in quartz, 

 obsei'ves : — "The mineral is crystallised at a high temperature, 

 say 150° C." (on Fluid Cavities).' The theory adopted by the Geo- 

 logical Surveyors often necessitates a temperature exceeding 365° C. ■ 



Since the publication of the Cornish Memoirs I have for the first 

 time understood the irritation that my unfortunate little papers have 

 naturally caused. St. Paul hits the position off exactly : " If I know 

 not the meaning of the voice, I shall be unto him that speaketh 

 a barbarian ; and he that speaketh shall be a barbarian unto me." 



I can assure my geological friends that for very many reasons 

 I most deeply regret ever having published outside the provinces 

 anything on the subjects of either Petrology or Pipplemark ; as both 

 subjects have led to a vast amount of genuine misunderstanding and 

 discomfort, and I may add of mystification ; and they are not 

 worth it. A. E. Hunt. 



ORIGIN OF THE SUDBUEY NICKEL ORES. 



Sir, — In Professor Coleman's interesting restatement of what he 

 regards as " incontrovertible proof " of the igneous origin of the 

 Sudbury nickel ores, he makes the safe assumption that I had not 

 seen the long announced second part of his monograph (Report of 

 the Bureau of Mines, Ontario, vol. xiv, No. 3). It would be 

 inexcusable for anj^one to discuss the Sudbury mining field without 



1 Reprint, p. 8. 



