294 ON THE TRANSMUTATION OF ROCKS, &c., 



It is not, therefore, surprising to find similar transmutations 

 in the heart of the Hawkesbury rocks. We have, indeed, near 

 Sydney some of the most remarkable transmutations which have 

 ever been submitted to the inspection of a geologist. 



There is a mass of white rock seen from the North Shore of 

 Port Jackson, on the top of the cliffs north of Bondi Bay, which 

 offers one of the most striking examples. This is finely depicted 

 in the photographs on the table. Again, near Botany North 

 Head, on the cliff near the old station, there is another example. 

 At Five dock is a third ; near Pyrmont there is a fourth ; on 

 Lane Cove a fifth ; and at Waverley there are traces of a sixth. 

 Others exist in the same formation on the Hawkesbury rocks, as 

 at the head of Cowan Creek, which I visited many years ago. 



In all these places the sandstones have undergone a great 

 change, and have become prismatised. 



The occurrence of prismatic sandstone has appeared to some 

 persons an anomaly. But it is not an uncommon feature in 

 sandstone countries of a geological age not widely distant from 

 the age of our Hawkesbury rocks. 



I have brought hither for comparison two prismatic examples 

 from the Hartz, from my own collection, and some others from 

 other countries. Nevertheless, this kind of structure is not 

 generally observable in the purest sandstones, and the prismatic 

 action is, therefore due, perhaps, to a molecular alterations as well 

 as to the element itself which holds the siliceous particles 

 together having been affected by heat. 



In some spots no trace exists visibly of the existence of basalt 

 or other trappean rock. But in others there is open to inspec- 

 tion a clear contact between them. Thus, below the cliff near 

 Bondi, which is a little north of that commonly known as " Ben 

 Buckler," (but which Mr. Hill tells me is a corruption of a 

 native word, "Baalbuckalea,") viz., at Meriberi, a mass of 

 basalt appears at the sea level and for a considerable height 

 above ; so that it is an intrusive dyke which only forms a boss 

 in that vicinity. Again, at the Sugar Loaf Hill near the Bargo 

 River, the boss of trap which forms that conical summit amidst 

 the bush is yet partially covered by transmuted sandstone in 

 situ, the relics of the masses that have been swept away. 



