BY THE REV. W. B. CLARKE, M.A., F.G.S., &c. 293 



the world. For instance, at the Giant's Causeway, in Ireland, 

 where basalt has overflowed chalk, there are deposits of lime ; 

 and between the basalt and a bed of rounded quartz and clay 

 which had covered the chalk before the outburst, crystals of 

 quartz and calc-spar occur in the cavities of the bed ; and a thin 

 layer of carbonate of lime is also formed. This carbonate of lime 

 is fibrous, just as the specimens are from the Pennant Hills 

 quarry. It fills in the interstices between the basaltic matter 

 just as it does in the latter place. 



In the neighbourhood of Camden, in some excavations made 

 for me many years ago in the presence of, and by the direction 

 of Sir W. Macarthur, I recognised a very much greater change 

 than this is at the junction of basalt with the Wianamatta 

 calcareous beds. Similarly at Burwood, near to the Railway sta- 

 tion, there is a fan-shaped mass of columnar basalt, which has 

 transmuted the soft shales of the Wianamatta series. There are 

 other places in Cumberland where basalt has risen and has 

 produced numerous examples of transmutation, just as under the 

 Mittagong Range the Wianamatta and underlying Hawkesbury 

 rocks have been changed. 



These latter deposits with which the remainder of my 

 remarks will be directly connected, underlie the Wianamatta beds, 

 and rise round them in a basin-formed trough between the sloping 

 edge of the coast district of Cumberland and the vertical escarp- 

 ment of the eastern edge of the Blue Mountain plateau. 



Denudation of a considerable extent had taken place before 

 the Wianamatta deposits began ; and, therefore, the basalts that 

 have altered both series must have been erupted more recently 

 than the latter. 



At points of junction of the two series, as on the west of 

 Prospect, I have come upon several instances in which the 

 Hawkesbury beds have been changed as much as the Wianamatta 

 beds, affording an exact parallel with the changes under the 

 Mittagong. 



In one of the specimens of the latter, you will observe that 

 the most siliceous rock has been partly vitrified, and is very 

 nearly allied in this state to some of the rocks from the Narran, 

 Darling, and Maranoa districts. 



