Abstract

During much of its development in the southern half of New South Wales, the Tasman geosyncline was divided by a ridge known as the Molong geanticline. This probably originated in the Middle Ordovician; it was certainly present from the Middle Silurian to the Middle Devonian, when folding ended geosynclinal deposition over much of the area. Its northern end is concealed by Mesozoic sediments; it extended southward for at least 65 miles, and may have reached as far as the Murrum-bidgee River west of Canberra—over 200 miles—or beyond.

Late in the Early Devonian, part of the ridge was land, fringed by a few bioherms, between and beyond which were deposited a variety of calcareous and terrigenous sediments making up the Garra Formation. The coral fauna suggests that this sequence is essentially Emsian in age. At the top there appears a distinctive fauna, named after the widespread Xystriphyllum dunstani, which correlates with a number of faunas in eastern Australia. This fauna, which contains occasional Calceola, probably appeared in the Late Emsian; its upward extension is not known.