THE GEOLOGY OF THE WHITE CLIFFS-Mt. JACK-PEEEY LAKE AREA, NEW SOUTH WALES J. Bade The Bade Stratigraphic Laboratory, Melbourne, Victoria (Plate vn) [Read 28th June, 1967] Synopsis The area lies north of the Darling River about 50 miles north of Wilcannia. Pleistocene to Recent, Tertiary, Cretaceous and Devonian sediments outcrop in the area. The hills in the Mt. Jack-Peery Lake area consist of Upper Devonian rocks. The Mulga Downs Group can be divided into the Momba Sandstone and the Paroo Sandstone. The main structural feature in the Mt. Jack-Peery Lake area is the Mt. Jack anticline. Two anticlines are present in the White Cliffs area. Palynological investigations show that the centre of the White Cliffs anticline consists of sediments belonging to Cretaceous Roma Formation, and the flanks of this anticline of Tambo Formation. Introduction The area considered in this paper lies in the north-western part of New South Wales ? north of the Darling Eiver and about 50 miles north of Wilcannia. Compared with the surrounding plains it is fairly hilly, the highest point being 725 feet above sea level. The average rainfall is nine inches per year, which produces semi-arid country with sand dunes ; however, the country supports some sheep and cattle. On geological grounds it may be divided into two regions : the Mt. Jack-Peery Lake area characterized by Devonian sediments, and the White Cliffs area where Cretaceous sediments are dominant with Devonian rocks outcropping only near its eastern edge (Fig. 1). Very little has been written about this area. Kenny (1934) mentioned it in describing the geology and sub-surface waters of the West Darling district ; Eelph (1959) described the White Cliffs opal field ; the author (Bade, 1964) described fish from the Mt. Jack-Peery Lake area, fixing the age of the sediments there as uppermost Devonian. Mulholland (1940) described the geology and underground water resources of the East Darling district, which contains Devonian rocks similar to those of the Mt. Jack-Peery Lake area ; the author (Bade, 1954) has described an area north of the Darling Eiver between longitudes 145° E. and 149° E. which lies to the north-east of the area considered in this paper. Geology Pleistocene to Eecent, Tertiary, Cretaceous and Devonian sediments outcrop in the area. Pleistocene to Recent These sediments consist of alluvium, clay, sand and gravel. Silt and mud are widely distributed on the plains and floodouts. Sand has accumulated in the flat valleys ; red sand dunes have been formed locally where sand has been derived from the disintegration of Devonian sandstones. The conglomeratic layers encountered in the Upper Devonian sandstones weather to sub-rounded quartz gravels, and the more resistant Upper Devonian sandstones form hard sandstone blocks. Tertiary The Tertiary is represented by sediments of the " Eyrian Series ", mostly shales and secondary quartzites which cap the Lower Cretaceous deposits in the White Cliffs area ; they are generally between 10 and 30 feet thick. Proceedings of the Linnean Society of New South Wales, Vol. 92, Part 2
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