J. Allan T/iO»ison — Diamond Matrices of Austmlia. 495 



12 miles south of Bingara, jS'ew South "Wales, and has also beea 

 described by Mr. Pittman.^ Ruby Hill, so named from the abundance 

 of garnets, is a small eminence of about 80 feet in height, formed on 

 one side by Carboniferous claystones and a quartz felsite dyke intrusive 

 into them, and on the other "by a volcanic agglomerate penetrated by 

 several basalt dykes. The map accompanying the description might 

 almost serve for one of the necks of East Fife. Both the agglomerate 

 and the dykes contain nodules of a rock consisting of garnet, anorthite, 

 and chrome-diopside, identified by Messrs. Card and Woolnough as 

 eclogite. Mr. Pittman draws an analogy betvreen the agglomerate 

 and the blue ground of Kimberley, but instead of following Professor 

 Bonney in ascribing the eclogite to waterworn fragments derived from 

 a floor of crystalline schists, suggests that it may be " the deep-seated 

 representative of the eruptives which found their way to the surface 

 in volcanic pipes at both these places ". 



Ten small diamonds were said to have been derived from Ruby Hill, 

 but latterly some doubt has been thrown on the genuineness of this 

 statement, since washing operations have not been successful in 

 bringing fresh specimens to light.- 



Still another supposed matrix is now being prospected at Snodgrass, 

 about 20 miles south-west of Delegate, New South Wales, close to the 

 Yictorian border.^ This rock, of which a poor exposure is found at 

 the contact of Silurian slates and sandstones and a granite intrusive 

 into them, is supposed to resemble blue ground in being composed of 

 angular fragments of various rocks lying in a serpentinous matrix, and 

 especially in the presence of eclogite nodules. As no diamonds have 

 yet been found in the rock or in any alluvial deposits in the district, 

 Mr. Pittman is justly doubtful of the probability of success in the 

 present explorations, but as will be shown in the sequel, his argument 

 that "in view of the authentic occurrence at Oakey Creek, near 

 Inverell, it seems more logical to search for diamonds, in this country, 

 in hornblende diabase " may need modification. 



It will be seen from the above account that Australian diamond 

 prospectors are inclined to attach much importance on the discovery 

 of blue ground, and further consider the presence of eclogite as an 

 important indicator. The latter predilection is owing to the well- 

 known discovery by Professor Bonney of diamond crystals within the 

 garnet of the ' eclogites ' of the Kimberley pipes. Messrs. Hatch and 

 Corstorphine * do not share Professor Bonney's view as to the importance 

 of these pyroxene -garnet nodules, and they, moreover, consider them 

 as related to the basic secretions of plutonic rocks, and not as true 

 eclogites. But even if diamonds are not plentiful in these nodules, 

 Professor Bonney's descriptions leave no doubt that they do occur 

 in them. 



I have already suggested that the nodules of crystalline rocks found 



' E. F. Pittman, " The Mineral Resources of New South Wales " : Geol. Surv. 

 .N.S.W., 1901, pp. 392-5. 



'^ E. F. Pittman, "Supposed Diamond - bearing Volcanic Pipe, Snodgrass, 

 N.S.W." : Australian Mining Standard, April 7, 1909, p. 359. 



3 Loc. cit. 

 o * F. H. Hatch & S. S. Corstorphine, The Geology of South Africa, 1905, p. 299- 



