24 



ON SOME IGNEOUS ROCKS FROM THE HEAZLE- 



WOOD DISTRICT. 

 By W. H.Twelvetrees,F.G.S., and W.F.Petterd, C.M.Z.S. 



Bead July 12, 1897. 



The Hecazlewood District is situated directly south-west 

 of the township of War at ah, in the county of Russell, and 

 has of late years been made fairly accessible in consequence of 

 its importance as an active centre of mining industry. The 

 geology is in several respects unlike that of any other 

 portion of the island, as far as known; though no system- 

 atic investigation of it has yet been undertaken. It lies 

 south of the great coastal basaltic sheet, and north of a series 

 of ancient metamorphic schists, with the interpolated gneisses 

 and masses of crystalline limestone of the Pieman River area. 

 Geologically, its characteristic features may be said to com- 

 mence at a locality situate on the main Waratah-Corinna 

 road, and known as the 10-Mile, and to continue thence to the 

 immediate neighbourhood of the 18-Mile Camp. It extends 

 in a northerly direction a small distance beyond Mt. Cleve- 

 land, and is crudely bounded on the south by the Parsons' 

 Hood Mountain, with an irregular interruption by the 

 stanniferous granites which form the main feature 

 of the Meredith Range. The characteristic which renders 

 the area of special interest to the geological student, and to 

 the petrologist in particular, is the occurrence of a series of 

 local rocks, which include fine grained granitites and syenites 

 with masses of serpentine, the latter being closely associated 

 with gabbros and ultra-basic rocks. These last commonly 

 appear as comparatively large intrusive dykes. Rocks of 

 the diabase and altered andesite families also occur, but are 

 by no means numerous. The granitites and syenites usually 

 form bosses of medium altitude, embracing and forming the 

 boundary lines of the intrusive serpentinised rocks, which are 

 remarkably pronounced on both sides of the Heazlewood 

 River. The gabbros are of several distinct types, and often 

 have their essential mineral constituents preserved in a very 

 fresh condition, although there is conclusive evidence that in 

 at least one instance the serpentine has originated from the 

 alteration of such a rock. In the limited class of ultra-basic 

 rocks we find a most attractive and varied series, such as is 

 rarely offered for petrographical investigation. These range 

 through the true peridotites to the varied mineral aggregates 

 of the pyroxenite family. In some instances only one of the 

 two crystal systems is present, but occasionally the rock con- 

 tains both the rhombic and monoclinic pyroxenes. In this 

 group also a considerable variation is noticeable in the state of 



