288 ON THE TKANSMUTATION OF ROCKS, &c., 



South Wales as at Worregee on the Shoalhaven, near Singleton 

 on the Hunter, and at Coyeo on the Page River there occur 

 many curious concretions of carbonate of lime simulating 

 crystals of selenite, but attached to each other in radiating forms 

 of very considerable size and thickness. In one instance the 

 substance is a marble, the molecular atoms having united in the 

 same way as in Carara or Pentelic marble. I found similar 

 concretions in the Carboniferous beds at Spring Hill in Tasmania, 

 not far from trap. 



No doubt these peculiar concretions have been formed under 

 some such agency as that which produces flints in beds of Chalk ; 

 but they are all examples of transmutation^ and as just such 

 spheroids as I have before mentioned are common in argillaceous 

 rocks in contact with trap, a low temperature may have assisted 

 in forming the lime concretions of the Carboniferous rocks. 



In the coal shale of the valley of D'All, in the Thuringerwald, 

 and in the upper Green sand of Cave Hill near Belfast, in Ireland, 

 are similar spheroids where the rock is in contact with trap. 

 But in the latter case the argillaceous odour remains with 8 per 

 cent, of water. Delesse figures an instance of felspathic rock in 

 the Yosges Mountains, which has been changed into parallellopi- 

 pedons which in the interior are perfect concentric spheroids. 



It is not surprising, then, that in other localities a true 

 prismatic structure should have been induced in argillaceous and 

 calcareous deposits, as in the beautiful columns of the South 

 Tyrol country. 



I would point out that in many of our Australian deposits we 

 find a tendency in the thinner portions to break off into geometric 

 forms having columnar divisions, with occasionally convex upper 

 surfaces ; and that at Point Puer, in Tasmania, in various parts 

 of Victoria, and about Wollongong and elsewhere, the rocks are 

 often jointed so as to produce a tesselated structure or miniature 

 representation of a " giant's causeway." In fact it is the pris- 

 matic structure, the joints being lined with ferruginous emanations 

 or deposits. 



Spheroidal forms appear to be common not only on earth 

 but in air and water. Vapour is suspended in spheroids held 

 up by electric agency, and owing to the same structure in the 



