This report presents the results of a gravity reconnaissance survey which was carried out under the writer's supervision during the last quarter of 1950. The report describes in some detail the methods adopted in carrying out the field work and the errors to which the results are subject. The results are discussed only briefly and the interpretation given must be regarded as a preliminary one subject to modification as further data are accumulated in extending or otherwise adding to the reconnaissance.

An earlier report (Record 1950/041) has described the geophysical survey carried out early in 1950 on the Renison Bell tin field. The present report deals with the work of a second field season which commenced in November 1950 and continued until June 1951. The methods used were again the magnetic and self-potential. The 1950 survey was extended to the south and east by continuing along the Renison Bell Hill base-line a further 1000 feet south and reading stations on both sides of this base-line along traverses extending from the main quartz-porphyry dyke to the headwaters of the Montana Creek. In addition, some of the traverses were extended over the saddle between Dreadnought and Stebbins Hills as far as the Boulder tramway. The report gives an account of the survey work and its results, and provides recommendations for future testing. The geological features of the area covered by the present geophysical survey are briefly described.

A provisional Isogonic Map of Australia and New Guinea for the epoch 1950.5 has been prepared by revising the observational material used in the Isogonic Map for 1942.5, and including observations made at various parts of Australia since 1942. The extensions of the Isogonic Lines beyond the coast line of Australia depend almost entirely on extrapolation from the earlier work.

The Mosquito Creek Wolfram Field was visited on 6th and 7th October, 1951. This report gives a brief account of the inspection. The general geology of the area, the ore-bearing reefs, and the mining leases inspected, are described.

The material described in this report was collected and forwarded for examination by Mr. M.R. Banks of the Geology Department, University of Tasmania. The report comprises notes on the lithology, fossil content, state of preservation, and correlation, of the samples.

A sample of lignite from a new water bore on the Freud River was sent for micropalaeontological examination. The results of the examination are described in this report.

At the invitation of Prof. S.W. Carey, the author visited Tasmania during the period 15th November to 2nd December, 1950, to take part in discussions on Cambrian geology in Tasmania and to learn in the field the results of recent investigations on Tasmanian older Palaeozoic rocks. During the visit the author had the opportunity of expressing his opinions both on newly discovered fossils and on the age of some Palaeozoic units, and the main object of this report is to record these opinions.

Towards the end of 1950, the deep bore which the Shell Development Company was drilling to test for oil on the Morella structure, 35 miles south of Rolleston, entered andesite at approximately 4000 ft. After boring about 200 ft into the andesite, the Company decided to abandon the hole. A new site for a test bore was selected on the Comet anticlinal structure, 60 miles north of Rolleston. Before proceeding with this new test, evidence was needed to ensure that neither a shallow basement nor volcanic rocks existed under this structure. The Bureau was therefore asked to shoot a refraction traverse over the anticline, in order to determine if basement rocks were likely to be present at a shallow depth. As a result the Bureau sent a seismic party to the area during January 1951. Fairly definite evidence was obtained of basement velocities occurring at a depth of less than 3000 ft, and after discussions, a decision was made not to proceed with the drilling of the Comet structure. The results have now been investigated in detail and are presented in this report.

For the purpose of obtaining further information as to favourable structural features in relation to brown coal seams within the Yallourn-Morwell-Traralgon area, a gravity survey is being carried out by the Bureau of Mineral Resources, Geology and Geophysics at the request of the State Electricity Commission of Victoria. In the following a preliminary interpretation is given of the results obtained by this survey to date. This interpretation includes a detailed correlation of the gravitational disturbances with the geological structures so far known. Practical experience to be gathered from the work so far done has been outlined.

This report is a detailed stratigraphical and structural study of an area of some 40 square miles south-east of Cobar together with a geological reconnaissance of an area of 500 square miles in the Cobar-Canbelego district. The purpose of these investigations was the elucidation of the general geology and the problem of ore localisation in the Cobar-Nymagee-Canbelego metalliferous province.