BY THE REV. W. B. CLARKE, M.A., F.G.S., &c. 297 



the occurrence of ferruginous patches cemented by silicic acid ; 

 these occasionally form veins or concentric curves. There is so 

 much in this account parallel with what may be seen in this 

 colony, and especially on Mount Victoria, where just such veins 

 occur in the sandstone, that it is a useful illustration of what we 

 find in Australia. 



Silicification has also produced kidney-shaped concretions of 

 jaspery quartz ; but sometimes, though rarely, there occur little 

 columns in the rock, slightly granular, of a white substance, 

 pulverulent, and having all the characters of alumina. These 

 prisms, which are quite distinct from the rock itself, are about 

 0.01. m. through, and 0.03 m. high. 



Springs are mentioned which are felspathised, and probably 

 rise from granitic rock below the sandstone. 



In many cases near Sydney, the cracks or fissures are, on the 

 contrary, lined with ferruginous matter, forming sometimes thick 

 casings, and, as on various points of the beach rock about Port 

 Jackson, on the coast to the north of Manly Beach and elsewhere 

 in the inner region, presenting dykes of ironstone which are not 

 always continuous for long distances, but which swell up into 

 bosses or irregular masses, as on the North Shore ; the entrance 

 of Middle Harbour ; head of Cowan Creek ; the Long Beef near 

 Narrabeen, &c. 



Other masses of hydrated oxide of iron occur at Brisbane 

 Water, at Fitzroy near the Nattai, and other places. 



The conclusions I have come to from a somewhat careful 

 examination of the whole of the localities mentioned and 

 numerous others, is that the Fitzroy iron ore is a product of 

 transmutation. 



The west end of the Mittagong is composed of a trachytic 

 rock, full of little crystals of specular iron. On it rest unaltered 

 the Hawkesbury beds. But these beds have been affected by an 

 after irruption of basalt, which there forms a considerable 

 portion of the range, and has produced a transmutation of the 

 sandstones and other rocks at the surfaces of contact. 



Springs have burst out at the junction of the formations, and 

 have brought up the iron and other minerals which are associated 

 with it, so that beds and stalactitical masses of the iron, originally 



