25 



preservation ; in some cases a pronounced chemical ehange 

 has occurred, whilst in others the rocks are in a perfectly 

 unaltered condition ; thus furnishing strong evidence in favour 

 of their intrusion at a later geological epoch. 



The sedimentary rocks are not extensively represented, so 

 far as observed. They consist of three distinct superimposed 

 beds, which are fairly well exposed in parts of the Bell's 

 Reward mine. The lower bed apparently rests mainly on 

 the granitoid rocks as a pale-coloured non-fossilised lime- 

 stone of some irregularity ; on this is a bed of sandstone 

 in which no fossils have been found. The whole is sur- 

 mounted by a layer of sandstone containing the casts 

 of numerous testacean remains, which show this formation 

 to be of silurian age. Occasionally, in other parts of the 

 district, argillaceous rocks are met with, but they are almost 

 invariably of limited extent. 



On account of the readiness with which many of the less 

 acidic rocks of the Heazlewood disintegrate and form soil, it 

 is often a most difficult matter to make a satisfactory ex- 

 amination, and it is thus needless to say that much work 

 remains for the field geologist, both as regards the relation- 

 ship and mode of occurrence of the rocks of both igneous and 

 sedimentary origin. This difficulty is further augmented by 

 the dense, in places almost impenetrable, nature of the 

 vegetation. In many localities, more especially on the banks 

 of the numerous small streams, there exists a somewhat heavy 

 overburden of tertiary sands, gravel, and clay, which, in 

 favourable places, have boen extensively worked for alluvial 

 gold. 



The series of rocks herewith described by no means 

 exhausts the petrological wealth of the Heazlewood, but an 

 endeavour has been made to present a fairly representative 

 series, taken from the rocks exposed by the construction of 

 the Waratah-Corinna road traversing the district. These 

 have been further increased by samples collected from 

 several of the silver-lead mines visited by one of the authors, 

 and by specimens received from the veteran prospector, Mr. 

 W. E. Bell. 



1. Harzburgite. 



Harzburgite : Eosenbusch, Massige Gesteine, 1896. p 355. 



Saxonite : Wadsworth. Lithological Studies, 1884. jp 85. 



Sp. Gr. 3 21. 



This is a typical peridotite, composed of olivine and 

 enstatite, harzburgite in accordance with the nomenclature 

 of Eosenbusch. Such rocks are not usually met with in 



D 



