180 PROCEEDINGS OF SECTION B. 



The order of crystallisation is actinolite, pyroxene, axinite, 

 quartz, chlorite, and lastly calcite. 



(b). Garnet- Vesuvianite-Actinolite Rock. — ^Traversing the bed 

 of Gormanston Creek (in the North Dundas tinfield) at a narrow 

 angle is a broad banded vein rock of variable composition, which is 

 undoubtedly genetically allied to the limurite. A great portion of 

 the vein is composed of felted actinolite, with which appear bands 

 or lenses of unreplaced slate and strong bands of garnet or vesu- 

 vianite rock. Small axinite veins have been seen in immediate 

 proximity to the lode. 



Pyrrhotite, haematite, chalcopyrite, sphalerite and sometimes 

 galena have been observed in association with the non-metallic 

 minerals. 



The actinolite shows features of similarity with that of the last 

 sub-group, but the type here described is separated from the 

 limurite on account of the presence of the garnet and vesuvianite. 

 The brown garnet is not abundant, but the vesuvianite rock is in 

 places massive. To the unassisted eye it has the appearance of 

 massive garnet rock. 



In thin section, however, the vesuvianite is at once recog- 

 nisable. It forms large crystals of negative sign, with the zones 

 and sectors characteristic of the species. The massive portions are 

 most markedly zoned where they have projected into druses and 

 the crystal terminations appear. Sometimes skeletal crystals are 

 visible, enveloping minerals which fill the veins traversing the 

 massive vesuvianite. Epidote, with pale brownish to greenish 

 yellow pleochroism tints, forms large euhedral crystals or small 

 anhedral grains. It is enveloped in the vesuvianite or projects into 

 the cavities, which were filled at a later stage. 



The later veins are of complex composition. Small euhedral 

 crystals of colourless fluorite are visible in some. Calcite is common 

 in the form of allotriomorphic plates, sheaves, divergent blades, or 

 small granules intermingled with quartz. The quartz fills the inter- 

 stices between the other minerals in single crystal plates or granular 

 aggregates. Chlorite is occasionally visible in nests of divergent 

 fibres which have the positive elongation and intense Berlin blue 

 interference colours of pennine. 



The normal crystallisation order is : Epidote, vesuvianite, 

 fluorite, chlorite, calcite, quartz. 



The association of this rock with the hmurite of Arbizon has 

 been noted by Prof. Lacroix^. 



III. — ^The Mode of Occurrence of the Contact Rocks. 



The rocks thus classified and described occur in the immediate 

 vicinity of the Devonian massifs of north-western Tasmania. They 

 are found enclosed within the boundaries of either the sedimentary 

 rocks invaded by the granitic magma or pre-granitic igneous rocks 

 of basic composition. 



1 Lnc. cit. ^upra. pp. r>6, ri7 .ind 6(1, 61. 



