BASALTS OF BATHURST AND NEIGHBOURING DISTRICTS. 305 
interlacing mass of fair sized crystals. Mr. Curran mentions 
how readily a slice of Bathurst basalt may be distinguished from 
that from Orange, even when the slice is still comparatively thick. 
This is certainly the case when we are making a section of Bald 
Hills basalt, but it is by no means so when the Apsley rock is 
compared with the Orange basalt. On the contrary, they are so 
much alike that one would think they came from the same place, 
and when I received the slides I at ea: sd iaoin-e a irae had 
been made in labelling them. Sul 
fresh pieces of Apsley basalt, it was found that they were all 
alike, and all differed from the Bald Hills rocks, In each case, 
as soon as a slice was thin enough to transmit light, one could at 
once say whence it had been obtained. Slides 1, 2, and 5, and 
the microphotographs similarly numbered, accompanying this 
paper, will shew what is meant. 
So marked a distinction between rocks obtained close together, 
naturally led one to try and account for the difference. The first 
idea that suggested itself was that the Apsley basalt might belong 
to a different flow of lava from that which covered most of the 
Bald Hills. Specimens collected from the most widely separated 
parts of the latter, have so far, however, failed to supply anything 
really like the rock from Apsley. Moreover, in chemical com- 
Position and specific gravity the two series of specimens agree 
very closely. The most probable explanation of the difference 
appears to be that it is due to different conditions of cooling. The 
felspars in the Apsley rock, besides being much larger, can be 
seen to intersect the olivine and augite crystals. There isa good 
deal of rather coarse magnetite between the other crystals, but 
not so much as in the Bald Hills rock, and scarcely any within 
the minerals themselves. There is little or no evidence of flow 
Structure. The rock on the whole appears to resemble the ophitic 
type of basalt, as figured by Professor Judd,’ rather than the 
granulitic, and the difference may be due to the Apsley rock — 
having solidified with little or no internal movement. 
1 Q.J.G.S., Vol. xu11. (1886), pls. v. and vi. 
T—Noy, 3, 18¢7, 3 
