17 
tained from the greenstone, the soils of this piedmont zone are, rela- 
tively, somewhat rich in plant food. The distribution of land suit- 
able for citrus fruits, limited on the west by a line approximating 
to the South-Western railway is determined by the extent of this 
zone. 
Each alluvial fan is slightly convex in profile and its stream 
occupies a notch on this convex surface. This introduces a tendency 
to instability of location of the channel, and there are probably in- 
stances of streams having left the convex surface to flow into the 
intervening hollows. Mostly, however, the streams occupy notches 
on the fans, a feature which is evidenced by the occurrence of the 
viaducts along the railway line at the summits of the grades in many 
instances. ( A very good example of this is at Keys brook. ) The outer 
margin of the piedmont zone is lobate, and cusps of the plain run in be- 
tween the lobes. The width of the belt varies considerably with the 
magnitude of the constructive streams, but is probably only from 
half to one mile on the average. 
( g .) The “Bandy Plain” follows the piedmont zone on the 
west. Into its constitution a number of sub-elements enter, whose 
relations vary considerably from point to point. As a whole the 
sandy plain is gently undulating, but quite sharp gradients are by 
no means infrequent. These are caused by the dominating structures 
of the region, namely, sand dunes of molian origin, geologically re- 
cent, but sufficiently old to have been fixed completely and perman- 
ently by the growt h of vegetation. Between these dunes there stretch 
low lying areas. During the extremely wet winter season the level 
of ground water rises to the surface in such localities, arid we have 
swampy areas filled with coffee-coloured peaty water. These swampy 
areas come to contain a moderate amount of clay substance and 
humus so that, when drained and cultivated, they become quite val- 
uable agricultural land, particularly for market gardens. The 
Chinamen’s gardens in the immediate vicinity of Perth are examples. 
Quite distinct Prom these smaller sporadic lagoons, there 
is a well-defined zone of large and shallow, hut more or less per- 
manent, lakes stretching along a north and south line between the 
hills on the east and the coastline on the west, including, amongst 
others. Lakes Jandakot, Bibra, Herdsman, Monger, etc. The origin 
of these lakes is under investigation and will form the subject of a 
further comm imi ration to the Society. Beyond the “Lake Zone” the 
sandhills of the plain continue to the west as they do to the east, 
hut they become more pronounced and individualised, probably be- 
cause more recent, in this western section. 
(//,) Forming a continuous belt facing the coast, rising into 
\ er\ respectable hills (Buekland ITill 207 feet), and projecting sea- 
wards as rocky headlands honeycombed with large and small cavi- 
ties, is the zone of “Coastal Limestones.” Formed by amlian action 
on the existing coastline, and composed largely of comminuted mar- 
