274 
Geology of Sydney. 
matic sandstone will point unmistakably to the 
proximity of masses of basalt. 
The Bondi basalt dykes have, it is evident, been 
one of the factors in the shaping of the present coast- 
line. In my opinion there are two separate intrusions, 
but not necessarily of different ages. The fissures at 
A, B, C, and E (see sketch map) are all belonging to a 
dyke which cut through the sandstones in a northerly 
and southerly direction. Besides the dyke running 
north and south, there exists a dyke, as described 
above by the Rev. W. B. Clarke, coming from the 
direction of Greenwich, and of which the basalt at D 
and G may be branches. 
The most notable feature of the locality is the 
columnar sandstone, as shown in Fig. 32. This struc- 
ture was, no doubt, induced by the proximity of the 
Igneous rock. Some of the sandstones that were in 
contact with the molten basalt show very little trace 
of metamorphism, while in other parts the same sand- 
stones are rendered quartzose in texture and prismatic 
in structure. No very clear relation can now be made 
out between the more extreme examples of metamor- 
phism, and any special massing of the Igneous rock. 
But denudation has so affected the locality that, at 
this date, it is practically impossible to say whether the 
basalt may not have almost surrounded the masses 
that show the columnar structure so perfectly. 
It may prove of interest to indicate here some of 
the lines along which a student may investigate the 
characters of this basalt. 
