388 Albert V. James: 



On' (/in of fht Bulla Kaolin. — Granodiorite may be kaolinized by 

 the action of meteoric water carrying carbon dioxide in solution, 

 which penetrating the granodiorite decomposes the biotite and 

 felspars. Kaolin in Fiji and the Dublin Mts (Ireland) is stated 

 by Prof. SoUas to have been formed in this way (12). 



Probably a commoner process of kaolinization and the proved 

 origin of the vast kaolin masises of England and Unitied States 

 (12 and 13) is that of pncumatolysis, where emanations of carbon 

 dioxide, boron, fluorine, or chlorine, probably with steam, have 

 decomposed the felspars and biotite of the plutonic rock. 



Threa investigators, E. J. Dunn, 1899 (15), R. W. Armitage, 

 1911 (U), and F. StiUwell, 1911 (11), have briefly discussed the 

 Bulla kaolin. While l>oth Mr. Armitage and Dr. StiUwell r>efer to 

 the possibility of either surface water or pneumatolysis being the 

 cause of the kaolinization of the Bulla granodioritte, the former 

 favouj's the meteoric origin and the latter the pneumatolytic origin. 



For the following reasons, it seems probable that pneumatolysis 

 and not meteoric water is responsible for the kaolin of this area. 



Evidence Against the Meteoric Theory. 



(a) Only Isolated Outcrops Occur in Victoria. — This is strongly 

 against the meteoric theory, for if the water and carbon dioxide 

 were subaerial one would expect kaolin to be found in all parts of 

 Victoria, where the old granitic surface is protected from denuda- 

 tion. 



(b) Only Isolated Outcrops Occur at Bulla. — There are about 

 ten outcrops at Bulla, and these are separated from one another by 

 solid, unaltered granodiorite. Generally the surface of the grano- 

 diorite is protected by basalt and gritstone,' and yet only rela- 

 tively Sirp,all outcrops of kaolin are found. 



(c) Relation of Kaolin to thie Sites of Old Valleys. — It has been 

 stated (14-) that the Bulla kaolin always underlies basalt which is 

 situated in the sites of old pre-basaltic valleys, and that the 

 drainage beneath and through the basalt Avould thus tend to be 

 gathered along lines where it could attack the granodiorite 

 vigorously. 



In reply to this it can be stated that kaolin does not always 

 underlie the basalt. In the largest Bulla quarry, Q^ the kaolin is 

 overlain by a considerable thickness of grits. The presence gener- 

 ally of basalt over kaolin is only what one would expect. Suppose^ 



