Somerville) the very evident higher level of the South Perth “raised” 
shoal, the levels of which can be clearly discerned from the junc- 
tion of Labouchere Hoad, Lyall Street and Mends Street. 
The second group corresponds to the Helena ( Vcle,, and in- 
cludes the shell beds of llinemoa lioek, M osman’s Bay, some of the 
higher shell beds at Cottesloe Beach, and the “raised’’ spits of 
Points Roe and Preston, and of Peppermint drove. The striking 
difference noticed by Somerville between the assemblages of shells 
in the beds of Mosman’s Bay and Minim dove has therefore a 
partial explanation if the cycles of rejuvenating movements he 
accepted. 
The first group falls into the Present Period, and embraces the 
lower shell beds of dottesloe Beach, and the associated “raised" 
platforms, part of Mill Point Spit, and the numerous “raised” 
beaches to be observed around the foreshores, at low elevations 
above high water mark. The last features have not been described 
in detail by Somerville, but are well developed, as, for instance, at 
Mends Street Jetty and at Applecross. These low “raised” 
beaches often bear a fi-tree and swamp flora. 
A most important formation, if eustatie movement is to be 
demonstrated, exists in t lie hidden shell banks of Perth and Melville 
Waters* These beds are covered by recent sand and mud, but 
are frequently revealed in dredging operations, and are so rich in 
shells that they are used extensively for road making and reclama- 
tion. A number of different species have been collected by Dr. 
E. S. Simpson, and determined by Mr. C. Medley of the Australian 
Museum, Sydney. Ostrea Angasi is the most abundant species. 
These shells are of the greatest interest, but we do not wish to an- 
ticipate Dr. Simpson or Mr. Medley in the description of the for- 
mation, though it is necessary for our purpose to make some refer- 
ence to it. None of the species is now existent in the neighbouring 
waters, the river indeed being almost devoid of mollusean fauna. We 
correlate the P&rth Shell Ranks with the Guildford Cycle, and believe 
them to be antecedent to the rejuvenating cycles. During the 
Guildford cycle the Swan broad waters were much more extensive 
than they are now* The effect of rejuvenation was to restrict the 
volume of the broadwaters, and to render the get-away of the winter 
floods more difficult owing to local constrictions of the channel, 
especially at the Narrows. The accelerated silting,, and lowering* 
of salinity which ensued assisted in extinguishing the fauna. The 
shells themselves, however, indicate also an important climatic change 
which is a necessary postulate in Daly’s hypothesis (18, 19). At 
Rathiest Island we correlate with the West Midland cycle the ob- 
scure high level platforms, To the Helena cycle are assigned the 
Rotlnest; Shell Ranks of the salt lakes, and their associated under- 
cut cliffs and elevated strand lines. It is possible that some of the 
