The Brown Coals of Cainozoic or Tertiary age in Australia are still but little advanced from the early stage, lignite. The leaves found in them are more or less like the present types of the flora. The wood is found to be of the Cypress type (Cupressinoxylon). In New Zealand, however, important deposits of coal of a more bituminous nature occur in the Oligocene of Westport and the Grey River Valley, in the Nelson District.
BONE BEDS.—The bones and excreta of fish and reptiles form considerable deposits in some of the sedimentary formations; especially those partly under the influence of land or swamp conditions. They constitute a kind of conglomerate in which are found bone-fragments and teeth ([Fig. 51]). These bone-beds are usually rich in phosphates, and are consequently valuable as a source of manure. The Miocene bone-bed with fish teeth at Florida, U.S.A., is a notable example. The nodule bed of the Victorian Cainozoics contains an assemblage of bones of cetaceans (whales, etc.).
Fig. 52—Bone Breccia, with remains of Marsupials.
About 3/4 nat. size. Pleistocene.
Limeburners Point, Geelong, Victoria.
(Nat. Mus. Coll.)
BONE BRECCIAS.—These are usually formed of the remains of the larger mammals, and consist of a consolidated mass of fragments of bones and teeth embedded in a calcareous matrix. Bone-breccias are of frequent occurrence on the floors of caves which had formerly been the resort of carnivorous animals, and into which they dragged their prey. The surface water percolating through the overlying calcareous strata dissolved a certain amount of lime, and this was re-deposited on the animal remains lying scattered over the cave floor. A deposit so formed constitutes a stalagmite or floor encrustation. As examples of bone-breccias we may refer to the limestone at Limeburners Point, Geelong ([Fig. 52]); and the stalagmitic deposits of the Buchan Caves.
IRONSTONE.—Rocks formed almost entirely of limonite (hydrated peroxide of iron) are often due to the agency of unicellular plants known as diatoms, which separate the iron from water, and deposit it as hydrous peroxide of iron within their siliceous skeletons. In Norway and Sweden there are large and important deposits of bog iron-ore, which have presumably been formed in the beds of lakes.