164 GREAT SERPENTINE BELT OP NEW SOUTH WALES, iv., 



In the quartz-magiietite-keratophyres, brecciation is rarely 

 seen. The vesicles are abundant, and are rounded or amygda- 

 loidal. All the magnetite seems to have crystallised in the 

 earlier period. As we pass to the quartz-keratophyres, there is 

 increasing evidence of the action of silicifying waters, not only 

 in the filling of the vesicles with quartz and chalcedony, but in 

 the attacking of the rock itself, the formation of rings of second- 

 ary silica, quartz or chalcedony around the original quartz-grains, 

 and the replacement of small parts of the rock-fabric by a fiinely 

 granular quartz (agate *?) mosaic. 



The jaspers associated with the keratophyres are the last pro- 

 duct of the spilite-keratophyre magma. Narrow veins of jasper 

 occur in the keratophyre, and large independent masses are 

 developed, which were deposited by successive bodies of siliceous 

 solutions, rising through fault-planes, metasomatically replacing 

 the country-rock, and depositing quartz and chalcedony, together 

 with the last of the iron-ore, now completely oxidised to haema- 

 tite. The last of the magmatic solutions, too feeble to form' 

 jaspers, have merely jasperised, and reddened, with haematite, 

 the banded radiolarian cherts. 



Thus the evidence of our magnetite-keratophyres series leads 

 to the conclusion that they primarily originated by magmatic 

 differentiation, but that hydro-pneuraatolysis played an important 

 minor role. This accords, to a great extent, with the views of 

 Hogbom, Stutzer, and Geijer, as to the origin of the Lappland 

 rocks. The structures developed have been explained as the 

 result of varying degrees of viscosity in the crystallising magma. 

 Recapitulating, we have the following table : — 



l.Pure albite-magma, with no vesicles or sign of pneumato- 

 lysis. Viscosity extremely high, amounting to partial rigidity; 

 brecciation a very marked feature. The trachytic structure is 

 probably the result of crystallisation under non-uniform pressure, 

 rather than actual flow. 



2. Albite-magnetite-magma, with a few irregular vesicles, and 

 slight evidence of pneumatolysis. Less brecciation than in No.l, 

 and more evidence of viscous flow. 



