large forarn. These beds show that the lakes were formerly less 
saline, and were connected with the sea. Their elevation above the 
present strand suggests that the closing of the lakes, and the union 
of two or perhaps three islands to form the present Rottnest, were 
effected by the rejuvenating movements. It also affords an ex- 
planation of the salinity of the lakes. The coast limestones are 
exceedingly porous, and the great loss of water from the lakes by 
evaporation during the hot and dry summer can only he counter- 
balanced by percolation of sea water through the limestone, which 
in turn implies continuous increase in salinity. The fresh water 
gained by the lakes during the wet winter is not competent, in our 
opinion, to maintain a balance with the sea. Two points of former 
union of the lakes with the sea are probable, one being at the 
eastern end of Government House hake, leading into Thompson 
Bay, the other being at the site of the proposed canal at the 
northern end of Lake Bagdad. The drift ini: of sand bars and dimes 
and the rejuvenating movements combined, we believe, in closing 
the lakes, and evaporation balanced by percolation from the sea has 
rendered them saline. Botli actions have caused the extinction of the 
shell fauna. 
GEOLOGY. 
The Crystalline Plateau . — The terraced segment of the Swan 
River is hanked on the east by the fault scarp of the Darling 
peneplain. The scarp has been described hv Jutson (10), and the 
features of the uplifted peneplain by Wooltiongh (Id). In the 
Guildford District, the plateau escarpment is composed of a variety 
of granites, which do not appear to show any clear marginal re- 
lationship to each other, one type grading im percept ib&y into the 
next. They are believed to be Pre-Cambrian in age, and are pene- 
trated everywhere by a plexus of basic dykes, here for the most 
part epidiorites, though dolerites are also known to occur. Further 
north, beyond Upper Swan, a gneissic series makes its appearance 
(9), but it has received little investigation. 
The Guildford Clays . — The Swan itself hows over the Guild- 
ford Clays from Upper Swan to Guildford. This formation extends 
right up to the foot of the Darling escarpment, and is claimed by 
Woolnough as part of a continuous piedmont apron (Id)* This view 
seems to he fully justified, but the relationship of the Guildford 
clays are not entirely apparent* They have claimed attention since 
1884, owing to their artesian water content* With their associated 
beds they form a distinct series, which we shall term the Guildford 
beds. They extend to a great depth, as is shown by the bore 
sections (8), and are of irregular character, without persistent 
horizons. They contain beds of hard sandstone in some places, 
but, as a rule, are not well consolidated. In lithological character 
they vary from red clays to sandy clays, gravels, sandstones, and 
