SUNKLANDS OF PORT PHILLIP BAY AND BASS STRAIT 93 
cycle.” Before the dune cycle, the period from the time the 
sediment commenced to accumulate in the headwaters of King 
Bay up to that when it was followed by another dune cycle may 
be referred to as the “hay bar cycle.” Tideways were formed 
connecting the land-locked waters behind the Bay Bar with the 
open Bay in front of it when the levels of each coincided. As has 
been stated, tideways, unlike river channels, have no gradients; 
such irregularities as do occur along their courses are caused by 
the encroachment of shifting shoals, or by constrictions in their 
channels. With the continued rise of sea level or slow subsidence, 
the tideways were submerged, fluvio-estuarine sediments were 
deposited along them, and in the Sorrento Bore shallow water 
limestone is found resting on the sediments. With the retreat of 
sea level, the tideways again functioned until the level of King 
Bay fell below the tideway bed. A new dune cycle then started, 
and dunes w'ere piled up, and encroached on the former tideways. 
There was no vertical erosion along the tideways when sea level 
was being lowered; the dune rock was too porous to hold up 
river or lacustrine waters. During the maximum rise of sea level 
there was a landlocked bay behind the Nepean Bay Bar, but this 
disappeared when the sea retreated — it never persisted as a lake 
or swamp. Only two swamps occur on the Nepean Peninsula — 
the Tootgarook Swamp and a salt lake near Sorrento; both are 
at sea level, and they probably owe their existence to the fact that 
sea level is the water table of the Peninsula. There are numerous 
“cups” with closed contours all above sea level, but none of them 
hold water or are their bottoms swampy. 
VI. Evidence in the Bores as to Tectonic Movements 
Excluding, for the time being, the effect of eustatic adjustment, 
the Pliocene, Pleistocene, and Recent deposits of the Sorrento 
and Wannaeue bores suggest the following tectonic movements : 
(a) Regional uplift terminating near the close of the Pliocene. 
(b) Pliocene-Pleistocene subsidence of the Bass Strait Sunkland accompanied 
by dune accumulation. 
(c) Period of standstill. Pluviatile erosion of the Dandenong Creek Cycle 
(pre-Newer Basalt). 
(d) Renewed subsidence of the Bass Strait Sunkland in the Middle Pleisto- 
cene to the extent of 170 feet accompanied by dune accumulation. 
(e) Period of standstill. Pluviatile erosion during which Dandenong Creek 
Cycle continued on the east side of the Yarra drainage system and the 
Post-Newer Basalt draining (Keilor Cycle) began on the west side. 
(f ) Commencement of the subsidence and tilting of the Port Phillip Sunkland 
near the beginning of the Upper Pleistocene. This movement has pro- 
ceeded to the extent of 100 feet and betrunked the lower portion of the 
Yarra River including the lower portion of Dandenong Creek and the 
streams that were developed on the Keilor and Werribee Plains lava fields. 
