Numerous Sponges of Silurian age are found in the neighbourhood of Yass, New South Wales, which belong to the Lithistid group, having irregular, knotty and branching spicules. These sponges resemble certain fossil fruits, generally like diminutive melons; their peculiar spicular structure, however, is usually visible on the outside of the fossil, especially in weathered specimens. The commonest genus is Carpospongia.
Receptaculites: Silurian to Carboniferous.—
In Upper Silurian, Devonian, and Carboniferous times the curious saucer- or funnel-shaped bodies known as Receptaculites must have been fairly abundant in Australia, judging by their frequent occurrence as fossils. They are found as impressions or moulds and casts in some of the mudstones and limestones of Silurian age in Victoria, as at Loyola and Wombat Creek, in west and north-east Gippsland respectively. In the Devonian limestones of New South Wales they occur at Fernbrook, near Mudgee, at the Goodradigbee River, and at Cavan, near Yass; also in beds of the same age in Victoria, at Bindi, and Buchan (Fig. 67, B.C.). Receptaculites also occur in the Star Beds of Upper Devonian or Lower Carboniferous age in Queensland, at Mount Wyatt. It will thus be seen that this genus has an extensive geological range.
Carbopermian Sponges.—
A Monactinellid Sponge, provisionally referred to Lasiocladia, has been described from the Gympie beds of the Rockhampton District, Queensland. Lasiocladia, as well as the Hexactinellid Sponge Hyalostelia, occurs in the Carbopermian of New South Wales.
Cretaceous Sponges.—
No sponge-remains seem to occur above the Carbopermian in Australia until we reach the Cretaceous rocks. In the Lower Cretaceous series in Queensland a doubtful member of the Hexactinellid group is found, namely, Purisiphonia clarkei. In the Upper Cretaceous of the Darling Downs District pyritized Sponges occur which have been referred to the genus Siphonia, a member of the Lithistid group, well known in the Cretaceous of Europe.
Cainozoic Sponges.—
A white siliceous clay, supposed to be from a “Deep Lead,” in the Norseman district in Western Australia, has proved to consist almost entirely of siliceous sponge-spicules, belonging to the Monactinellid, the Tetractinellid, the Lithistid, and the Hexactinellid groups ([Fig. 69 A, B]). The reference of the deposit to a “deep lead” or alluvial deposit presents a difficulty, since these sponge-spicules represent moderately deep water marine forms. This deposit resembles in some respects the spicule-bearing rock of Oamaru, New Zealand, which is of Miocene age.