458 Norman Taylor — The Cudgegong Diamond-Field. 



Why are diamonds, if drifted, so vai'iable in size, being often 

 larger down the river than nearer their supposed source ? 



Why are diamonds, nearly always, more or less contorted from the 

 true octahedron, forming oblique octahedrons ? 



Why are the diamonds, when they occur in the largest quantity, 

 both larger and purer than when in small quantity ? 



Why are diamonds locally variable in aspect, one spot turning out 

 straw -yellow coloured gems, another with internal black spots, and 

 another perfectly pure ? 



Any answer to the above queries must of necessity lead to the 

 conclusion that the diamonds have been formed in situ in the older 

 drift. The writer, for his own part, believes that the so-called asso- 

 ciation of other gems with the diamond is purely accidental, that 

 these gems occur at the bottom of the older drift, with the gold ; the 

 diamonds occurring at irregular depths above it, and their associa- 

 tion being merely due to the miners taking out some six feet or more 

 of the drift, and thereby bringing them together in the process of 

 washing. 



All the extracts brought forward by the late Eev. W. B. Clarke, in 

 his Presidential Address to the Royal Society of New South Wales, in 

 May, 1870, 1 only prove that a large amount of unreliable and un- 

 reconcilable data have been collected, which add little or nothing to 

 our knowledge of the true matrix of the diamond ; and, as to how 

 the diamond has been formed, taking this gem as an illustration of 

 the purest form of the element carbon, as little is known or likely to 

 be, as there is of any of the other- elementary substances. Until 

 chemistry throws some light upon the possible modes of formation 

 of the diamond in nature, and demonstrates the necessity of its 

 occurrence in metamorphic rocks, it is perhaps as easy to suppose 

 that the gem may originate in a late Tertiary drift deposit, as in the 

 most ancient strata of a somewhat similar origin. Quartzites and 

 quartzose conglomerates occur in Australian Tertiary deposits having 

 as highly metamorphosed an aspect as those in the Silurian rocks. 

 If the diamonds have been formed in the older drift, it will account 

 for their absence in the present river-bed ; on the other hand, if the 

 diamond has been drifted from its original matrix, either it might be 

 expected to occur in the river, where it has never yet been detected, 

 or, its matrix has been entirely denuded away in older Pliocene or 

 earlier times. Large areas of Carboniferous and older strata, as well 

 as extensive tracts of Tertiary basalt, have disappeared from the river 

 basin ; and some persons have therefore proposed to assign the 

 original position of the diamond to local and limited deposits in the 

 demolished Palaeozoic rocks. 



1 See Trans. R. Soc. K S. Wales for 1870, pp. 1—48, " On the Discovery of the 

 Diamond in N. S. Wales ;" and Ibid, for 1872, pp. 1—66, " On the Natural History 

 of the Diamond." — R. E., jun. 



