STUDIES IN HYDROTHERMAL ALTERATION 199 



tion seems necessary that since pure water has practically no effect 

 on the feldspars, and that since the alkaline waters produce minerals 

 other than kaolin, kaolin probably forms by the action of acid solu- 

 tions upon the feldspars. The literature bearing on the field occur- 

 rences of kaolin shows a striking lack of references to association of 

 carbonates and kaolin, though this would be expected if carbonated 

 waters are the cause of the formation of kaolin from the feldspars. 



6. The general agreement of the data obtained throughout the 

 range of temperatures used shows that the silicates may be studied 

 with the apparatus described, up to 300 C, with gratifying results 

 and without great mechanical difficulties, and also without the 

 necessity of contamination from undesirable sources such as glass 

 tubes. 



The writer is indebted to Professor W. H. Emmons for suggest- 

 ing the problem and to Professor A. D. Brokaw for sincere interest 

 and many suggestions during the progress of the work. Further 

 work of a similar sort is in progress and the next paper will deal 

 with the action of various acid solutions, especially hydrofluoric 

 acid on the same group of minerals. 



