BY FRITZ NOETLIKG, M.A., PH.D., ETC. 95 



with the breccia, is a really micro-crystalline porphyry 

 of yellow colour. It is impossible to decide these ques- 

 tions without a microscopical examination, but should 

 this be carried out the most interesting results are cer- 

 tain to be obtained. 



I determined the specific gravity of ii different 

 pieces, which gave the following figures : — 



1. Red Breccia, Drouglity Point 2.540 



2. Brown Breccia, Droughty Point 2.588 



3. Grey Breccia, Droughty Point 2.590 



4. Red Breccia, Drought}^ Point 2.610 



5. Brown Breccia, Droughty Point 2.616 



-6. Brown Breccia, Droughty Point 2.621 



7. Red Breccia, Bellerive 2.653 



8. White and Black Breccia, Mona Vale .... 2.654 



9. Grey, Streaky Breccia, Droughty Point . . 2.655 



10. Red Breccia, Droughty Point 2.686 



11. Brown Breccia, Droughty Point 2.782 



The average specific gravity is 2.636, but it does not 

 seem that there is a connection between colour and 

 specific gravity. The range is apparently a much smaller 

 ■one, as there is only 0.242 difference between the lightest 

 and the heaviest variety examined. 



4. OTHER SILICEOUS ROCKS NOT IN- 

 CLUDED UNDER THE ABOVE HEADINGS, 

 SUCH AS CHALCEDONY, OUARTZ, WOOD 

 OPAL, FOSSIL WOOD. 



This group includes rather a heterogenous mixture 

 of siliceous minerals, which have been provisionally 

 placed together. It is remarkable to note that not a 

 single implement made of any of this mineral has come 

 under my notice which shows a good finish. All the 

 specimens are of the very crudest type, and generally 

 mere fragments only. The reason is obvious. None of 

 them except wood opal shows that fine conchoidal frac- 

 ture which is so essential for a good tronatta. Chalce- 

 dony in its numerous varieties has a very splintery, 

 rough fracture, which is still stronger in the ordinary 

 quartz. Wood opal has a fine conchoidal fracture, but 



