SUNKLANDS OF PORT PHILLIP BAY AND BASS STRAIT 89 
places in the Inner Basin, near the south-east slope of the Nepean 
Bay Bar. The holes are due to the turbulence of the tidal streams, 
and are referred to here as “scour holes.” They are assumed to 
be formed by the eddying of sti'eams after they pass from a 
contracted tideway into a basin. Their formation is complicated 
by several factors, but it is beyond the scope of this contribution 
to consider such. It is apparent, however, that they may be 
formed by either the in-going or out-going streams, after they 
have passed from a tideway into a basin. 
The scour hole (Fig. 6) at The Heads is roughly crescentric in 
shape, with the end in Port Phillip pointing E.b.S. towards the 
South Channel, and the end in King Bay pointing S.S.E. In 
Port Phillip, it occupies a position in the fairway between The 
Heads, midway between Point Nepean and Point Lonsdale; 
between the Nepean Peninsula and Shortland Bluff, it widens 
out into a deep basin with an average depth of 54 feet formed 
by the convergence of West, Symonds and the South Channels. 
Its deepest part is W.N.W. of Point Nepean, where it has a 
depth of 282 feet (47 fath.) ; it shallows quickly to the E.N.E., 
and where it turns to the S.S.E. At this S.S.E. extremity, there 
is a reef with, at places, less than 28 feet of water over it. This 
reef, which is responsible for the rip, slopes to the north into the 
scour hole ; its slope to the south is part to the steadily deepening 
profile of King Bay. 
The in-going tidal stream comes from the southward and 
eastward, increases in strength as it nears The Heads, sets right 
across the entrance, across through the reefs with great force, 
and spreads towards Shortland Bluff and Point King (Fig. 7) ; 
past that point, in the South Channel, it sets E.N.E. across the 
Middle Ground and through the Pinnace Channel (Fig. 7). The 
out-going stream from the Inner Basin passes obliquely through 
the various channels, the stream from Symonds Channel joining 
and turning that of the West Channel below the Royal George 
Shoal, setting towards the bight between Shortland Bluff and 
Point Lonsdale, and from thence through The Heads, the body 
of the stream setting athwart the entrance towards Point Nepean 
and away south-eastward along and into the shore between Point 
Nepean and Cape Schanck, Knowing the directions of the tidal 
streams both inside and outside The Heads, it is obvious how the 
scour hole became crescentic in shape. The fact that the King 
Bay coast E.b.S. of Point Nepean is young has already been 
mentioned; it is inferred from the position and direction of the 
scour hole that at its S.S.E. extremity it was formed in a tideway, 
and the coast formerly extended as far out, at least, as this. 
