BY THE BEV. W. B. CLARKE, M.A., F.G.S., &c. 295 



There, all the changes are easily traceable from unaltered to 

 highly vitrified compact beds ; the basalt itself having in all its 

 features, especially the calcareous portions, the closest re- 

 semblance to the Pennant Hill rock. 



Again, at the lately boasted-of gold diggings on a branch of 

 the Nepean River, a few miles from Mittagong village, I 

 found the whole of the drift in which the few particles of gold 

 dug there were found, composed of most highly transmuted 

 fragments of true Hawkesbury sandstone. I broke with my 

 hammer a -very great number of these pebbles accumulated in 

 heaps, and I am quite sure, that no other drift than that exists, 

 and in one of the creeks near by I picked up basalt. 



Another example of a similar kind to that of Bargo exists 

 about a quarter of a mile west of the lock-up on the Berrima 

 Road, near the Little Forest, where a mass of basalt stands in 

 the midst of a denuded area, the sides and summit bearing 

 altered fragments of the same Hawkesbury rocks. Most 

 beautiful dendritic oxidations of manganese occur on some of the 

 faces of rough basaltic blocks. Most of our Hawkesbury rocks, 

 especially near to Sydney, are poikilitic, i.e., they are variously 

 coloured by the oxidation of iron, the hues of which have 

 changed from the usual ferruginous colour of rust, to yellow, 

 reddish, and grey, not always giving an agreeable tint to our 

 public buildings. Take the Exchange, for instance, and other 

 edifices in Sydney, where dull-coloured dark grey and yellowish 

 toned stones occur in no definite arrangement with the rest. 

 Again, most extraordinary forms are occasionally represented by 

 the distribution of the iron in some blocks of stone ; and it 

 appears that whilst the saiad was moist or friable enough to allow 

 ferruginous impregnations to pass downwards in successive 

 layers, or after all these were deposited, another series of white 

 laminae not at all disarranging the former, have crossed them 

 apparently at about equal consecutive intervals of time. Any 

 one who will go about the city and inspect the walls of houses 

 and other buildings, will find plenty of good examples. 

 Occasionally, the forms referred to take the character of a 

 landscape, resulting from a combination of lines and colours. 

 Witness the stone fairly representing a hilly island, over the 



