452 Transactions. — Geology. 



termed schistose. The various mineral layers blend into each other, and 

 are composed chiefly of quartz, felspar, mica, and talc or chlorite, while 

 veins of quartz ramifying through clay, slate, or other non-siliceous rock, 

 render them convertible into argillaceous mica-schist or phyllite, mica-schist, 

 granulite; or less siliceous kinds, forming talc, chlorite, hornblende, or 

 actinolite-schist, or schorl rock. 



Schistose structure has been found also to be occasionally produced in 

 lavas, the vesicles in which have been compressed and attenuated in the 

 direction of flow (Eutley, Q.J.G.S., vol. xxsvi., p. 285). 



A further alteration of these rocks takes place into gneiss, which has a 

 schistose structure, the quartz, felspar, and mica, and often hornblende, of 

 which it is composed, being arranged in layers, the foliation constituting 

 the chief difference from granite. Gneiss, and schistose rocks, with inter- 

 calated beds of crystalline limestone, form the laurentian rocks of Canada. 

 The schist containing beds of graphite, or unoxidized carbon and apatite, 

 (Dawson, Q.J.Gr.S., vol. xxxii., p. 285), denotes plant, and the limestone, 

 animal life. Graphite occurs also at Pakawau, in Nelson, under similar con- 

 dition in metamorphosed strata, and its presence denotes that no extreme 

 temperature was attained during metamorphosis of the rock. 



Gneiss has been found in many cases to merge into granite, so that the 

 extreme of metamorphism may be regarded as granite, the fundamental 

 rock throughout our earth ; and its massive crystalline texture and its 

 chemical combination of elements, namely, quartz, felspar and mica, must 

 now be regarded as the ultimate crystalline condition, under great pressure, 

 of sedimentary strata, either by slow consolidation after having been con- 

 verted into a molten state, or by gradual chemical and structural change. 



The quartz in granite often has cavities and enclosures of other minerals, 

 principally rutile and chlorite ; these cavities generally contain pure water, 

 occasionally liquid carbonic acid,, or a solution of chloride of sodium ; 

 they also contain bubbles, or rather vacuous spaces which show the con- 

 traction which the imprisoned fluid has undergone during the cooling of 

 the rock. Dr. 8orby and others have endeavoured to calculate the amount 

 of pressure shown by these contractions in volume. Spaces or beads of 

 glassy or amorphous quartz, also occur, which denote that the quartz had 

 first become viscous, and in consequence solidified without crystallizing. 

 The liquefaction proved by the liquid cavities to have once been the condi- 

 tion of granite, has caused it in places to burst through adjacent rocks in 

 an eruptive manner, when disturbed perhaps by an increased pressure, 

 while other portions of the same mass may gradually blend into schistose 

 sedimentary strata. Professor Judd has proved how granitic rocks in the 

 Island of Mull, Scotland, and at Schemnitz, in Hungary, are directly con- 

 nected with volcanic rocks, and both form portions of one and the same mass. 



