o88 Albert V. James: 



Origin of tht Bulla Kaolin. — Graiiodiorite 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 ami the Dublin Mts (Ireland) is stated 

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



Probably a conmioner process of kaolinization and the proved 

 origin of the vasi; kadlin masses of England and Unified States 

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

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

 decomposed the felspars and l^iotite of tlie plutouic rock. 



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

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

 Bulla kaoliir. While both Mr. Armitage and Dr. Stillwell nefer tO' 

 the possibility of either surface water or pneumatolysis being the- 

 cause of the kaolinization of the Bulla granodiorite, the former 

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



For the following reasons, it seems probable that pneumatolysis 

 and not meteoric Avater is responsible for tlie kaolin of this area. 



Evidence Against the Meteoric Theory. 



(a) Only Isolated Outcrops Occur in Victoria. -^lliis is stroiigly 

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

 were subaerial one would expert 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 sniall outcrops of kaolin are found. 



(c) Relation of Kaolin to the 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 would thus tend to be 

 gathered along lines whei'e 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 oyer kaolin is only what one would expect. Suppose- 



