Basalt. 
259 
by tlie list given below, unaltered basalt is not at all 
plentiful, the dykes being usually changed to a soft 
clay. Thus it is that we value every evidence of the 
former presence of the fiery masses that intruded the 
sandstones and shales from unknown depths. Pris- 
matic and hardened sandstones are accepted as almost 
conclusive evidence of the proximity of basalt, and, in 
making a record of the occurrence of basalt, we find 
it almost of equal value to make a record of the pre- 
sence of prismatised and altered sandstones. 
Intrusive masses, mostly in the shape of dykes, of 
undecomposed basalt are known around Sydney at — 
1. Prospect Reservoir. 
2. Pennant Hills quarry. 
3. Dyke running east and west at Rook wood. 
4. Moorefields dyke, Canterbury, running in a 
north-easterly and south-westerly direc- 
tion. 
5. Basaltic dyke at Peakhurst, probably a con- 
tinuation of the Moorefields dyke. 
G. Dyke at Bondi, on the coast, running north 
and south. 
7. Dyke at Long Reef, between Narrabeenand 
Manly, probably a continuation of the 
Bondi dyke. 
8. Dyke at the head of the small bay between 
Long Bay and Maroubra Bay. 
9. On Humphrey’s property, Burwood,abasaltic 
dyke was quarried some years ago. 
10. In a brick-pit, St. Peters. 
