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websterite, a remarkable, coarse, diallage rock with subordinate 

 enstatite, and of an unusually rare rock called rodingite, which 

 has an exceedingly high lime-content (31-01 per cent.) and a very 

 high specific gravity (3-502). 



Hutton originally described the rodingite as a saussurite gabbro, 

 a name by which it continued to be known for many years, but 

 Bell, Clarke, and Marshall determined the supposed saussurite as 

 grossularite (lime- aluminium garnet), and introduced a new name, 

 "rodingite," for the rock. The coarse greenish-white crystals of 

 the grossularite are moulded on subordinate diallage, which is practi- 

 cally the only other constituent, and often show alteration to a 

 mineral identified as prehnite. The normal rodingite occurs as more 

 or less narrow dykes intrusive throughout the general peridotite, 

 but varieties termed "prehnite rodingite" and " serpentine-prehnite 

 rodingite," in which prehnite has replaced the original grossularits, 

 form an important belt separated from the eastern margin of the 

 peridotites by a strip of sediments over half a mile wide. 



In discussing the origin of the rodingite, Bell, Clarke, and 

 Marshall reject any possibility of assimilation of adjacent limestone 

 by the magnesian magma, and suggest some form of differentiation 

 as the controlling cause. 



A chrome-iron ore, or more strictly a spinelled mineral inter- 

 mediate between chromite and picotite, forms separate grains in the 

 dunite and serpentine, and is frequently segregated in the latter 

 to form nodules and small, discontinuous, scattered, lens-like veins 

 which furnished nearly 4,000 tons of ore before mining operations 

 were abandoned in 1866. The Dun Mountain tramway, a popular 

 route to the top of the mountain, was built in order to transport 

 this ore. 



Copper lodes occur in shear-zones in shattered serpentine, and in 

 the Dun Mountain area are found chiefly near where the serpentine 

 merges into the dolerites and diorites forming the western margin 

 of the " Mineral Belt." The lodes are numerous but highly dis- 

 continuous, and only a comparatively few feet in greatest dimension. 

 After a long unprofitable struggle since 1855 against unfavourable 

 conditions, mining practically ceased about twelve years ago. The 

 site of the most important operations was in the valley of Roding 

 River, a few miles south-west of Dun Mountain. In this area the 

 gangue is chiefly serpentine or occasionally rodingite. The un- 

 oxidized ore shows two main associations cupriferous pyrrhotite 

 (containing up to 1-5 per cent, of copper) and minor chalcopyrite, 

 both intimately intermixed, or else pyrrhotite and native copper. 

 In both the pyrrhotite is the earlier mineral, and the presence of 

 native copper with it is ascribed by the authors of the Dun Mountain 

 bulletin to differential oxidation of the pyrrhotite.. though the con- 

 ditions permitting such oxidation are not stated. The same writers 

 consider that the lodes are genetically connected with the intrusions 

 of rodingite. 



The oxidized superficial portions of the lodes show the usual 

 minerals, and from some of the outcrops large blocks of native 

 copper have been obtained. 



Mr. C. P. Worley states that specks of platinum have been found, 

 as might be expected, in the alluvium of some of the streams draining 

 the peridotite belt. 



J. A. BARTRUM. 



