THE AUSTRALIAN NATURALIST. 29 
ABSTRACT OF LECTURE ON GEOLOGY OF SYDNEY. 
(By W. N. Benson, B.Sc.) 
Mr. Benson likened the geological deposits of the Sydney 
district to a pile of saucers with Sydney at the centre and 
this district in Permo-Carboniferous times, the sea washed 
Newcastle, Lithgow, and Nowra situated near the rim. Over 
and icebergs deposited stones on its floor. These sea-de- 
posits form what is called the Lower Marine Series. The 
sea gradually silted up and became a great marsh on which 
grew enormous fern forests ; the land was slowly sinking and 
these fern forests formed the Greta coal seam. Again, the 
sea washed over the district, the deposits this time forming 
the Upper Marine Series. Once more it was silted up and 
again forests grew. The land slowly settled and the buried 
forests became the Newcastle coal measures. At this time 
there was great volcanic activity at Murrurundi on the North 
and Kiama on the south, and vast quantities of volcanic mat- 
ter were ejected and washed down by streams and rivers. Then 
followed in Trias-Jura times the deposition of the Narrabeen 
shales and conglomerates, the materials probably coming from 
the north-west. Volcanic dust forms the chocolate shales of 
Narrabeen and Stanwell Park—a strata which carries a char- 
acteristic vegetation. Then followed a change of drainage 
and the formation of the Hawkesbury sandstone, the material 
for which came from the south-west. The final series was a 
lake deposit, the Wianamatta shales. 
By means of lantern slides the lecturer showed specimens 
of fossil ferns—Glossupteris and 'hinnfeldia— numerous shells, 
fish antl the Labyrinthodont. 
In ‘vertiary times came the uplift of the Blue Mountains 
and the volcanic activity which produced the dykes and necks 
at Hornsby, Prospect, Dundas, Bondi, and other places. The 
Jecturer showed excellent views of the prismatic sandstone 
at Bondi. He referred to the sinking of the land by which 
Sydney Harbour was formed and the Hawkesbury River Val- 
ley inundated by the sea. 
‘he producuion of sand beaches and spits and the present 
form of the coast-line has been the work of a recent geological 
period. A slight elevation of a few feet has been converted 
into dry land. An instance of this is Manly, where origin- 
ally North Head was an island. 
The lecturer was warmly applauded at the close of his 
most interesting lecture. 
THE PRESIDENT AND MRS. FROGGATT’S 
“AT HOME.” 
June.—The members of the Naturalists’ Club were invited 
to an ‘‘At Home,” at ‘‘Bonito,’’ Croydon, the residence of 
