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its thickness is therefore doubtful. From the surface down to 3 feet the 
diatomite is in a partially decomposed and impure condition. It is highly 
jointed, and infiltrating water, bearing ordinary humus acids from the 
decomposing vegetation, has so acted upon it that its value is much 
decreased. The remaining 2 feet visible comprises diatomite of purer 
quality, though this also is much jointed and stained with oxide or iron in 
the joints. Doubtless lower down the material is much better, but nothing 
definite can be said about its quality as a whole until it has been pros¬ 
pected by bores and shafts. Decomposed bas.alt evidently occurs all around 
it, for though neither this nor the diatomite is visible at the surface, owing 
to the covering of soil, still among the roots and mounds of fallen trees the 
decomposed basalt may be seen, andl the margin of the diatomite was ap¬ 
proximately defined bv testing with a spade. There is no surface indication 
to distinguish the diatomite from the decomposed basalt, and the deposit 
was discovered only when sinking post-holes for the boundary fence crossing 
it. It undoubtedly, at this spot, is not covered with anything but surface 
soil, composed of a mixture of decayed vegetation and diatomite. This 
fact shbws at once that, in the absence of an overlying impervious stratum, 
all water falling on the surface soaks rapidly down through the porous 
material, conveying humus acids which continuously act upon it, and 
decompose it, while roots of trees disintegrate it to such an extent that all 
the upper porti'co is practically valueless. Its occurrence on an almost level 
plain surrounded by decomposed basalt, and its limited extent, suggest that 
it was formed either in a rock-hole or depression on the surface of a lava 
flow which, on the solidification of the lava into basalt, had an impervious 
floor in which water permanently lodged, or in a depression containing 
a hot spring, thus admitting of the continued growth and decay of the low 
forms of vegetable life possessing siliceous structure from which the material 
has been dierived. Similar rock-holes, with and without water, are now 
visible among the “ Stony Rises ” at Pirroo Yallock, near Colac, while 
others, varying from a few feet to 50 feet in depth, and a few yards to scores 
of yards in breadth, occur in various parts of the Portland district, and also 
in many other volcanic districts in Victoria. If this view is correct, numer¬ 
ous other similar deposits probably occur distributed over the volcanic plains 
of the district. Their size and value will, of course, depend) upon the size 
of the original hollows, whether as rock-holes, lakelets or dams; the per¬ 
manence of the conditions respecting the growth of the necessary forms of 
vegetation; and the presence or absence of a protective covering. 
About 6 chains to the N.W. of this deposit, I found two small pieces 
of what looks like decomposing diatomite among the roots of an uprooted 
tree. This is apparently separated by decomposed basalt from the deposit 
described, as far as can be ascertained by testing the' intervening area with 
a spade, and the mounds, of uprooted trees. If, therefore, it is diatomite 
it probably indicates a similar occurrence, but of unknown size. This 
material is now being further tested. 
Assuming the deposit to be the shape of a truncated inverted cone, with 
a basal diameter of 120 feet, and a smaller diameter of about 100 feet, and 
taking it to be 15 feet th'ck, the lower portion (10 feet) to be diatomite of 
value, and the dry weight, that given to me by Mr. Ewen Cameron, M.P., 
viz., 25 lbs. per cubic foot, it contains about 900 tons of diatomite of value. 
This, at £1 per ton, said to be the local price of the material, would indicate 
a sufficient inducement to thoroughly prospect it by boring or shaft sinking, 
preferably the former, on the score of despatch and economy. A small, light 
hand-boring plant, capable of boring to 25 or 30 feet, would answer the pur¬ 
pose of proving the deposit. It should first be tried with the ordinary twist 
auger, like a wood auger, which would extract a core sufficiently good to show 
