254 
The following is the analysis of a sample from this deposit, made at 
the Mines Department Laboratory by Mr. L. G. Benjamin: — 
No. 602 . % 
Silica (Si 0 2 ) ... ... ... ... 74*34 
Alumina (A 1 2 0 3 ) ... ... ... ... 8*36 
Ferric oxide (Fe 2 0 3 ) ... ... ... 2*66 
Lime (CaO) ... ... ... ... — 
Magnesia (MgO) ... ... ... ... — 
Soda (Na 2 0 ) ... ... ... ... *09 
Potash (K 2 0 ) ... ... ... ... *02 
Water (H 2 ) at 100 ° C. .., ... ... 9 12 
Water combined ... ... ... ... 4*91 
9950 
This indicates diatomite of better quality than that of samples B and C 
from the Bolwarra deposit. 
Diatomaceous earth is used for various purposes—as an absprbent for 
nitro-glycerine in the manufacture of dynamite, when it must be in a pure 
state; for packing for boilers and steam pipes, owing to its non-conduction 
of heat; as polishing powder; as light fire-bricks, because of its lightness 
and infusibility; in the manufacture of water-glass and soap, on account 
of its solubility in alkalies. In view of its value andt the increased attention 
that is being paid to it in Victoria, I should strongly advise local people to 
make a careful examination of the volcanic portion of the district, when I 
have no doubt other deposits will be found. In prospecting for it here, 
special care should be taken to examine all water-channels, every fragment 
of coherent earthy material seen, and all mounds of uprooted trees. If these 
mounds show anything definite, then with a spade the hollows in which the 
trees stood should be tested. This will be a much quicker and less laborious 
method than digging at random over a large extent of obtuntrv. 
Diatoms are of common occurrence in some of the younger geological 
formations,, such as those of Upper Cainozoic to Recent age. Most of them 
are aquatic in habit, and live in fresh, brackish or salt water, either of high 
temperatures as in the hot springs of volcanic districts, or of low ones as 
the very cold water of glacial lakes. There are between i,ooo and 2,000 
known species,, and by virtue of their remarkably rapid development they 
form, under suitable conditions, and in a short space of time, geolog cally 
considered, deposits of considerable thickness, such .as that at Richmond, 
Virginia, U.S.A., which is 40 feet thick, and extends over a considerable 
area. 
General Geology of the Portland District. 
A brief description of the general geology of the Portland district is 
given in the following notes : 
The oldest visible formations are friable white and yellowish limestones, 
that show from 10 to 35 feet thick in coastal cliff sections in the town of 
Portland, from the railway station along the shore of Portland Bav for 
about twb miles to the north. These contain a few fossils, principally 
echinoids (sea urchins), brachiopods (lamp shells) and whalebone, which 
show the deposit to be of early Cainozoic age, probably Oligocene or Eocene. 
Th : s deposit is of great thickness and extent; it underlies all South-Western 
Victoria. In Portland, it has been proved to have a thickness of at least 
