306 W. J. CLUNIES ROSS. 
Passing on to the Mount Pleasant rock, there is not much to 
say. It is finer grained than the Apsley and than most of the 
Bald Hills basalt. Mr. Curran describes and figures it as a micro- 
- porphyritic rock similar to that of the Bald Hills. He says he 
has about ten sections. I have only one good section and that is 
somewhat weathered. It is not decidedly porphyritic and shews 
only slight indications of flow structure. It rather suggests a fine 
grained edition of the Apsley rock. In view of Mr. Curran’s 
greater experience of the rock, however, it is possible that my 
section is not typical. 
CHEMICAL CoMPOSITION. 
The only analysis of the Bathurst basalt with which I am 
acquainted is a very complete one by Mr. Mingaye, of the Mines 
Department, quoted by Mr. Curran.* My own determinations 
agree fairly well with his, except that I make the percentage of 
silica rather more, and that of the alumina rather less. My 
results are as follows :— 
From the Bald Hills, Corporation Quarry, I obtained silica 
47°75 per cent. From the small quarry near Perth, at about seven 
hundred feet, 47:55 per cent. Mount Apsley, mean of three 
determinations, gave 48°2 per cent. Mount Pleasant gave 4 
higher result, 49-8 to 50 per cent. 
Alumina, Bald Hills, 18-5 to 19 per cent. Apsley 17°5 to 18 
per cent. Mount Pleasant 15-5 per cent. 
Ferric oxide, Bald Hills, 12°5 to 15 per cent.; Apsley 14:5 per 
cent.; Mount Pleasant 14:5 per cent 
Lime, Bald Hills, 8-4 to 10°6 per cent.; Apsley 10-08 per cent.; 
Mount Pleasant 7-5 per cent. — | 
Magnesia, Bald Hills, 7-5 to 9-2 per cent.; Apsley 6-86 to 7°56 
per cent.; Mount Pleasant, I did not obtain a satisfactory result. 
Considerable variation was noted in the percentage of bases, 
and this is only what one might expect in a porphyritic rock, a8 
2 Geology of Bathurst, p. 57. 
