97 
person foolish enough to tread upon it. 
The species of diatoms in closely situated swamps varies 
considerably. In any one of them from ten to thirty different 
species may be recognised. A point which needs elucidation is 
the exact conditions which lead to these immense accumulations 
of such minute objects. 1 have noticed in many cases that the 
deposits are thickest at the northern ends of the lakes. One side 
of Lake Joondalup is formed of the coastal limestone, which 
probably accounts for the diatomaceous earth in this deposit 
being contaminated with shell fragments and calcareous mud. 
In 1903 the whole of the north-western portion of it was burning 
steadily down to a depth of several feet. A white moss-like 
growth of a Chara covers a large part of this deposit. 
Thompson Lake and Bibra Lake, at Jandakot, to the south 
of Fremantle, are, like the Wanneroo swamps, filled with diato- 
mite. They are for the most part dry during the latter part of 
the summer. 
Similar deposits exist further south. A large stretch of 
swampy country to the south of Grasmere, near Albany, has been 
drained recently and put under cultivation. A very pure dia- 
tomaceous earth covers the greater part of it to a depth of several 
feet, and as at Wanneroo makes an excellent soil for market gar- 
dens, because of the large amount of nitrogenous organic matter 
associated with the siliceous diatom frustules. Similar material 
has also been sent to me from the vicinity of Busselton , and from 
Cape Arid, between Albany and Esperance. It should be sought 
for in any swamp in the south-west where the surrounding soil 
is sandy. 
Diatomaceous deposits occur under rather diff erent conditions 
in the Irwin River valley, east of Dongara. this country is 
largely occupied by the so-called “ sand plains -in reality not 
plains at all, but rolling moorland, the soil of which is composed 
principally of coarse sand derived from the locally developed 
soft sandstones and grits of Carboniferous and later age. 1 his 
country is for the most part very dry, but is dotted with oases 
where the scrub gives way to larger and more luxuriant vegeta- 
tion. Within these oases the ground is constantly kept moist 
by subsurface springs of water, rich in silica derived from the 
sandstones through which it has filtered. Under these conditions 
diatoms grow abundantly (associated more 01 less with Iresh 
w ater sponges) and form deposits of diatom eaith at times seveial 
feet in thickness and covering many acres of ground. Many of 
the diatoms in these deposits are quite distinct from those in 
the south-western districts. Mingenew Spring and Irwin Spring 
are typical localities. The deposit at the latter point caught hie 
early in 1902 and burnt steadily for something like six months, 
much to the astonishment of local residents. In burning it gave 
rise to thick sublimates of ammonium chloride. 
