Geological Progress. xxxi 



The important branch of Vulcanology has made an invalu- 

 able addition to its literature, with the publication, by the 

 Royal Society of Great Britain, of the report of its Committee 

 upon the Krakatoa eruption. That body comes to the 

 conclusion, that the extrusion of the volcanic matter of an 

 eruption is due, not to the presence of water in the magma, 

 but to the occlusion of potentially gaseous compounds, formed 

 by chemical interaction between some of the heated minerals. 

 This important generalisation has been dubbed the "Cartridge 

 theory," as it pre-supposes that there are in the crust of the 

 globe certain strata which, being heated, generate within 

 themselves explosive gases, which thereupon rend the over- 

 lying rocks, and then by their expansion, expel the molten 

 magma in which they are entangled. According to this 

 view, the paroxysmal outbursts which so frequently mark 

 volcanic emissions, are due to the accidental admission to 

 the^ lava of quarry water, which nearly always saturates 

 all the rocks forming the walls of the upper part of the rent- 



Another subject which was discussed at the recent 

 Geological Congress, is the nature and origin of the 

 crystalline schists. Whilst a great diversity of opinion 

 prevailed between the greatest living geological authorities, 

 in relation to many important but open questions bearing 

 upon this class of rock, the tendency of the discussions 

 reveals a widely held belief that the schistose characteristics 

 of gneiss have been developed by the dynamic strains 

 incidental to the process of mountain building ; and also, 

 that any kind of rock subjected to this intense pressure 

 may be transformed into gneiss, whether it be of sedimentary, 

 organic, or plutonic oiugin. 



These matters are the principal points which come under 

 notice in reviewing the geological progress made during the 

 past year. 



