94 ROCKS USED IN THE MANUFACTURE OF TRONATTAS. 



The fracture is splintery, and, though a little con- 

 choidal, the breccia does not flake as well as hornstone 

 or porcellanite. 



Like porcellanite, the breccia never develops a 

 patina, but when exposed to blown sand it takes a fine, 

 smooth polish. Fire acts differently on oreccia — in fact 

 the result is more like that of chalcedony than of either 

 hornstone or porcellanite. The whole specimen is 

 covered by numerous cracks, intersecting each other in 

 all directions, but apparently not penetrating deeply into 

 the interior. 



Breccia is much less frequently used for implements, 

 then either of the foregoing rocks, and I never found a 

 specimen showing careful chipping on the indical face. 

 All tronattas consisting of breccia are of the crudest 

 types. I think that this is due to the inferior qualit}' of 

 die fracture, but in particular to its splintery nature. 



Breccia does not seem to occur very frequently. 

 Only one actual outcrop is known to me, at Droughty 

 Point. The rock occurs here in large, loose blocks and 

 boulders, lying near the shore on the top of a volcanic 

 rock. There is no doubt that this occurrence has been 

 made use of by the Aborigines, though it cannot be 

 termed a regular quarry, but the ground close to these 

 boulders contains a large number of implements which 

 have been manufactured from this breccia. Mr. Stephens 

 kindly told me that there is another occurrence near 

 Ulverstone, and it appears that the tronattas found near 

 Devonport were derived from that source. 



Geologically speaking the breccia is perhaps the 

 most interesting of all. There can be no doubt that the 

 Droughty Point breccia must be considered as a de- 

 posit of hot springs. In fact it is a silica sinter, as is 

 conclusively proved by the fine banded texture of the 

 matrix. 



On the other hand, the beautiful black and white 

 breccia from Mona Vale appears to be a true breccia 

 porphyry. Here the molten magma penetrated through 

 a conglomerate, breaking it up into angular fragments, 

 which floated in the magma, and became thereby meta- 

 morphosed. It further appears that a certain group of 

 '.rocks found near Margate, which I provisionally classify 



