On the Occurrence of the Diamond near Mudgee. 105 



hypothesis on the origin of the diamond, which is so rare in 

 comparison. But there are one or two facts about the diamond 

 which do not equally apply to the other associated minerals. 

 First, the diamonds are never waterworn, and very seldom 

 fractured, while the sapphire and all the other gems are rolled 

 excessively. The superior hardness of the diamond may account 

 for this peculiarity. A few shapeless ones have been found, but 

 if their want of crystalline form is due to abrasion, the lustre 

 has not been in the least impaired by the process. Secondly, 

 they are not so uniformly distributed as the other gems^ but 

 generally occur in rich patches, and wherever most abundant 

 they are also largest and purest. The diamonds found at the 

 Two-mile Flat are larger than those found at Wialdra Creek, 

 which is higher up the river. These and other facts have led 

 some to believe that the diamonds actually grew in the drift. 

 The structural planes in many of the crystals also suggest this 

 belief; but, if such is the case, those who hold this view cannot 

 explain why diamonds do not occur in similar drifts which are 

 common throughout Victoria, and in other parts of this colony. 



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 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 times. Large 

 areas of Carboniferous and older strata, as well as extensive 

 tracts of tertiary basalt, have disappeared from the river basin ; 

 others have therefore proposed to assign the original position of 

 the diamond to local and limited deposits in the demolished 

 palaeozoic rocks. 



The fact of the association of the diamond with other gems, 

 which are mostly derived from igneous or metamorphic rocks, 

 does not prove that they came from the same rocks. Innumer- 

 able creeks and rivers in the colony contain abundance of fine 

 sapphires, topazes, zircons, &c., but do not yield the diamond. 

 Beechworth in Victoria, the Macquarie, the Turon (Stutchbury), 

 Calula Creek and the Cudgegong Eiver in !New South Wales, 

 and, we believe, Hahndorf in South Australia, are almost the 

 only Australian localities where the diamond is at present known. 



