Page:Cyclopedia of Western Australia, volume 1.pdf/47

The coals of the Collie field are hydrous, semi-bituminous, non-caking coals, which approach very closely to lignite in some parts; between the various varieties the differences are only of degree. So far as departmental analyses indicate it appears that the average calorific value of the Collie coal is about 10,000 British thermal units. According to estimates which have been made it seems that, omitting the seams of trifling thickness, there is about 137 ft. of coal in the 2,072 ft. of strata so far explored by mining and boring operations.

Estimates have been made as to the quantity of coal available in the seams so far known, and these are given in the following table:–

The coal production of the State up to the end of 1910—which is entirely that of the Collie coalfield—amounts to 1,778,158 tons valued at £822,424.

Jurassic, Tertiary, and Post Tertiary lignites and brown coals, mostly of poor quality, are known to occur in various portions of the State, but so far little active work has been done upon any of them. No geological surveys have yet been undertaken such as would enable even an approximate estimate to be made of the area or quantity of coal available in these Mesozoic, Tertiary, and recent strata.

Salt.—Salt is obtained from certain depressions in the calcareous sandstones of the coast, which are filled to a shallow depth in winter with salt water. In summer lakes of this type dry up completely, leaving a layer of salt 2 or 3 in. thick, which is collected and either consumed locally or exported both as a fine and a crude product. The four localities where salt collecting has been carried on are at Rottnest Island, off Fremantle; Middle Islands, near Esperance; Yarra Yarra Lakes, near Three Springs; and Lynton, near Port Gregory.

There is a very large number of salt and brine lakes in many districts in the State, but their geographical situation and other causes place them at present beyond the reach of profitable enterprise. So far as records are available it appears that about 3,500 tons of salt valued at £8,525 have been produced in the State up to the close of 1910.

Phosphate Deposits.—The occurrence of phosphatic fertilizers has such an important bearing on the future of the agricultural industry that considerable attention has recently been paid to the discovery of these substances. The known phosphate deposits of Western Australia are distributed principally in two localities:—(a) The islands along the coast and (b) a portion of the Coastal Plain between Dongara and Perth.

Up to the present time the chief source of the guano raised is in Houtman's Abrolhos Islands, which lie about 30 miles north-west of Geraldton. That the importance of these deposits is considerable may be judged by the fact that up to the end of 1903 86,165.25 tons of guano valued at £335,591 were exported from the State and a royalty of £41,955 paid to the Government. The guano deposits in these islands are nowhere very thick, varying from 4 to 27 in.

No estimate of the supply of guano on these islands is available, though the last surveys made some years ago showed the available tonnage on several of the islands to amount in the aggregate to 100,490.

Christmas Island in the Recherché Archipelago, about 20 miles south-east of Israelite Bay, contains a fairly large area of phosphatized limestone, which rests upon a foundation of granite. The phosphatized limestone has an average thickness of about 2 ft.

In the neighbourhood of Dandaragan, about 22 miles to the west of Moora, is a series of low hills containing phosphate deposits. These occur in beds which have been followed across country for a distance of about 22 miles, and the rock phosphate is exposed in several places. There appear to be three distinct classes of material among the phosphate deposits, viz., (a) weathered rocks containing from 0.54 to 2.10 per cent, of phosphoric acid; (b) ferruginous sandstones containing phosphates mainly of iron, with from 7.25 to 15.13 per cent. of phosphoric acid, the iron phosphates occurring as dufrenite and vivianite; and (c) fossil bone and coprolite rock containing from 15.32 to 39.34 per cent. of phosphoric acid. The bone-bed has been proved to be about 3 ft. thick, and the underlying ferruginous sandstone, which has been more or less phosphatized by the interaction of ironstone and phosphoric acid derived from the bone-bed, is at least 7 ft. in thickness. The bone-bed is the most important of the deposits, and it is possible that judicious prospecting may result in the discovery of portions much richer in phosphoric acid than any of the outcrops yet tested.

In addition to these rock phosphates there are at Watheroo some cave deposits consisting of evacuations of wallabies, bats, and birds, some of which is of high- grade quality. The value of deposits of this nature depends upon the extent of the caverns and the quantity and quality of the accumulations contained in them. The comparatively recent cave limestone country which extends practically from Geraldton southward along the