minent physiographic line, and their parallelism and serial arrange- 
ment call lor an explanation which we believe is given by the re- 
juvenating movements which affected the Perth District. The ex- 
planation we shall give of the Rottnest lakes confirms our opinion 
concerning the Bunbury lakes. 
The Islands off Fremantle . — Garden Island, Carnac, and Rott- 
nest represent a former westward extension of the coastline, and 
were probably separated from the present coast by local subsidence 
(10). They are formed of Coast Limestone (a consolidated, car- 
bonate dune reck) and of recent sand dunes. Pott nest, which en- 
closes a group of salt lakes, gives very clear evidence of having been 
affected by rejuvenating movements. 
The whole island is surrounded by a reef, or wave-cut plat- 
form, which extends for half a mile or more to sea, where it ends 
abruptly, being undermined by the waves. The solid reef limestone 
appears to rest on unconsolidated sands. At high tide it is covered 
by three to four feet of water off-shore, whence it shallows 
gradually to the shoreline, where it ends usually in a beach, or on 
headlands and exposed places, against low, undercut cliffs of lime- 
stone. It is tile product of recent wave action, with a very low 
wave base, owing to the shallowness of the surrounding sea. The 
modern beaches are often bordered to landward by a low raised 
beach, indicating a movement of about eight feet. An older, ele- 
vated platform replaces the raised beaches on the rocky shores and 
stands about four feet above high water mark. There is also indi- 
cation of a platform about twenty feet above high water mark, but 
owing to the rapid wcatheiing of the coast limestones under wind 
and rain, and to the encroachment of recent dunes, this high-level 
platform is very obscure. Where recognisable, it often carries 
fragments of large shells upon its surface. One such platform exists 
at the northern end of Thompson Bay, and another extends from 
Xmicv Gove to the Eastern end of Strickland Bay. The platforms 
arc interpreted as elevated reefs. 
The shores of the salt lakes expose a most interesting section 
com | osed almost everywhere of consolidated shell beds, which extend 
to greater heights than the present shores of the lakes, and end 
frequently against undercut limestone cliffs, the bases of which are 
about eight feet above high water mark. Elsewhere the shell beds 
extend far inland, marking former extensions of the lakes, as at the 
north end of Garden Lake. In a few places, the beds mark old 
shorelines at a greater height than eight feet, as at Padbury’s flat. 
The shells are very abundant, and are well preserved, the two 
valves of ] elecypods often being united. The shells belong to 
existing species, and form a very different assemblage from that 
of the shell beds of Perth and Melville Waters. Associated with 
the Rottnest shells are one eelunoid, one serpulid worm, and one 
