BY R. H. CAMBAGE. 



443 



somewhat unusual feature is the presence of hypersthene in some 

 quantity. 



I am indebted to Mr. J. C. H. Mingaye, F.C.S., for the follow- 

 ing analysis in which the high percentage of silicon may be 

 noted :— 



Eock No. 6693 in Geological Survey Collection. 





Weight 







Weight 





Percentage. 







Percentag 



Si0. 2 



... 66-06 



CI 





... o-oi 



A1 2 3 



... 15-25 



S(FeS 2 ) 





... 0-06 



Fe 2 3 



... 1-10 



Cr 2 3 





... None 



FeO 



... 3-69 



NiO, CoO 





... 0-02 



MgO 



... 2-27 



MnO ... 





... 002 



CaO 



... 4-86 



BaO ... 





.. 0-06 



Na 2 



... 2-16 



SrO ...Ti 



ace (spectroscopic) 



K 2 



... 2-77 



Li a O ... 





. . . None 



H 2 O(100°C) .. 



... 030 



V 2 3 ... 





... 0-03 



H 2 O(100°C + ) 



... 094 



Copper 





. . . Trace 



co 2 



... 007 



Lead ... 





... Trace 



Ti0 2 



Zr0 2 



... 0-70 

 ... 0-03 













100-51 



P 2 s 



S0 3 ... 



- ll 









... None 



Specific Gravity 



... 2-726 



Gold — A few g 



rains per ton. 



Silver — 4dwt. 8gr 



per ton. 



Analysis 2479/19 



06. 





J. C. 



H. Mingaye 



It is of interest that this hard porphyritic rock should contain 

 an appreciable quantity of silver, as it is in this same igneous 

 area at Yerranderie near Burragorang that rich silver lodes are 

 being worked. 



The gravel along the banks of the Nepean near Penrith, which 

 provides Sydney with some of its very best road metal, is derived 

 from the waterworn fragments of rocks in this and a somewhat 

 similar geological area on Cox's River. 



With this change in geological formation as well as in aspect, 

 a considerably different flora from that of the sedimentary 

 plateau is found, as expected. Sheep are seen grazing over the 

 rocky areas, which at once suggests western conditions, and soon 

 the interest of the botanist is intensified by the sight of plants 

 which more properly belong to the western slopes beyond the 



