THE AUSTRALIAN NATURALIST. 45 
EXCURSION TO BONDI. 
Tux excursion to Bondi on Saturday, September 3rd, was 
under the leadership of Dr. I. H. Jensen and the party pro- 
ceeded from the Bondi tram terminus direct to the spot where 
occurs the interesting mass of columnar sandstone. 
imity of an intrusive mass of basalt, to the heat and pressure 
of which the columnar structure is supposed to be due, was 
pointed out. Dr. Jensen gave an interesting general account 
of the geology of the district, explaining how the beds of 
shale which are found intercalated with the Hawkesbury 
standstone, owe their origin to past sinking of the land where- 
by shallow lagoons were formed in which the shale material 
was deposited and how a saries of successive risings and 
fallings had brought the strata to the positions in which 
they are now found. 
The prox- 
Incidentally the leader pointed out the interesting sandhill 
which is gradually encroaching on the land lying between 
Bondi and Rose Bay, and which is fed by sand blown over 
from the ocean beach. 
Attention was also directed to the great Notonectian (south- 
flowing) current which is well-marked by the trend of the 
muddy water entering the ocean from the main sewer at 
Bondi point. The party descended by the track leading from 
the quarry, where the columnar sandstone was formerly 
worked for road-metal, over the cliff to the outfall of the 
sewer. A thick bed of shale is here exposed in section and 
numerous minor dykes are to be seen cutting the disturbed 
strata in various directions. 
Following the line of cliffs in a southerly direction several 
gaps leading down to the water were explained as being the 
spaces formerly occupied by basalt dykes, which, being less 
durable than the sandstone, had been completely weathered 
out. One long dyke runs for a considerable distance in the 
same direction as the coast line near the edge of the cliff and 
having been much-weathered presents the appearance of a 
deep, wide, straight-sided furrow. 
A visit was paid to the flat surface of the cliff just to the 
north of Bondi Bay where some rude outlines of fish, 
made by the aborigines, were seen. The leader also 
remarked that it had been pointed out by Mr. G. A. Water- 
house that the dykes occurring along the coast in this dis- 
trict, when traced outwards are found to come to a focus at 
one or other of two points in the ocean, the principal one of 
which has been proved by the ‘‘Challenger” and other sound- 
ings to be a submerged peak, probably a centre of extinct 
