Geomorphology

Igneous rocks of basic character dominate the Central Plateau. A great dolerite sheet of Jurassic caps the Plateau and forms its resistant surface. Later, sporadic basalt lavas of Tertiary age fill old drainage depressions cut in the Plateau. The dolerite is far more voluminous, but less varied in its chemical composition (approx. 1500 cu. km; silica range 52-60%) than the basalts (approx. 15 cu. km; silica range 36-53%). Both these rocks express important events which affected the Southern Hemisphere. The dolerite is the vast molten response to initial fracturing of the southern supercontinent, Gondwanaland, of which Tasmania is a small fragment. The basalts form part of the eastern Australian volcanic province which erupted in response to warping, stretching and increased heat flow along the continental margin as sea-floor spreading opened up the Tasman Sea and Southern Ocean, beginning about 85 million years ago

A Darwin manuscript on Hobart Town

The collection of Darwin's papers in the Library of Cambridge University includes a 22-page manuscript on the Geology of Hobart Town. Consideration of the manuscript suggests that Darwin's collection of fossils described in 'Geological Observations'came from the Bundella Mudstone at Porter Hill, the Cascades Group near Barossa Road, Glenorchy, and the Malbina Formation at Eaglehawk Neck. The manuscript further demonstrates his assiduity and acuteness as a geological observer, and suggests a considerable fund of geological knowledge Of Van Diemen's Land in 1836

Mr Gordon Hale 1921-2004, Honorary Life Member, Royal Society of Tasmania: Obituary

Gordon Hale was born in Hobart on 19 June 1921 and died in Hobart on 18 August 2004. During his lifetime he knew severe hardship but gave much to theTasmanian community through his profession as engineering geologist, through active membership in professional societies, including the Royal Society ofTasmania, and in war veterans' bodies. He was widely respected

Preface

The Lake Country of Tasmania - high, flattish and bejewelled with lakes - is unique in Tasmania and even in Australasi

General geology

We may think of the Plateau as consisting of two main, nearly horizontal, layers of rock resting on a basement of older, steeply tilted rocks. The surface layer, a few hundred metres thick, is dolerite about 165 million years old. This was injected into marine and non-marine sedimentary rocks deposited during a span of about 90 million years beginning about 290 million years ago. The part of this sequence originally over the dolerite has been removed by erosion, that beneath the dolerite is preserved as an almost continuous band around the northern base of the Plateau from Travellers Range to Table Mountain. The basement consists of metamorphic, sedimentary and igneous rocks some older than 570 million years, intruded by granite over 480 million years ago and again about 345 million years ago, and folded into a mountain range about 370 million years ago

Obituary, Samuel Warren Carey, AO, 1911-2002

The Royal Society of Tasmania lost one of its members of long standing on 20 March 2002 when Emeritus Professor Samuel Warren Carey died in Hobart at the age of 90

A type section of the Permian system in the Hobart Area

An unbroken succession of Permian sediments about 1430 feet thick on the northern flanks of Mt. Nassau, about 10 miles north-west of Hobart, Tasmania, shows the following succession of formations from the base upwards: Bundella Mudstone; Faulkner Group including the Geiss Conglomerate, Rathbones Sandstone and Siltstone, Byers Sandstone, Jarvis Siltstone, Parramore Sandstone and Siltstone, Altamont Conglomerate and Fergusson Siltstone; Rayner Sandstone; Cascades Group including the Nassau Siltstone, Berriedale Limestone and Grange Mudstone; "Woodbridge Glacial Formation"; Risdon Sandstone and finally the Ferntree Mudstone. These range in age from Lower Artinskian to Kungurian. These formations, except the "Woodbridge Glacial Formation", are defined. The Faulkner Group consists of two cyclothems, recording two brief emergences, one soon after the other,in a time of general submergence. The Grange Mudstone and Berriedale Limestone are at least partly facies variants of one another. A notable feature is the presence of erratics, except in the two non-marine formations in the Faulkner Group, and this is perhaps related to the poor sorting, and mineralogical immaturity of the sediments and the angularity of most of the grains in all rocks. All of these features are considered as the result of glacio-marine deposition. The source area included granitic, sedimentary and regionally metamorphosed rocks

Charles Darwin's field notes on the geology of Hobart Town- a modern appraisal

A transcription of unpublished field notes made by Charles Darwin details the observations and initial deductions he made on the geology of Hobart, Tasmania, and comments thereon place his work in a modern context. The field notes enable the routes of his excursions while in Hobart Town to be inferred in considerable detail and confirm earlier ideas about the site from which important fossils were collected. They also allow some appreciation of Darwin's style of geological study. Darwin's field notes reveal that he thought of the possibility of the influence of earthquakes on Tertiary beds at Sandy Bay. Several of his ideas on the geology, shown by these notes, some of them also in his publications (e.g. the origin of a Tertiary freshwater limestone, and relative movement of the land and sea in the area), remain topics for further study. His work in the Hobart area and his understanding of the geology of Van Diemen's Land were enhanced by contact with George Frankland, Surveyor-General, who had a long-term and systematic interest in the topic. The notes formed the basis ofa geological "Memo on Hobart Town" and, later, two publications, each work having a different purpose and emphasis. His work near Hobart did not produce enough information for the construction of a stratigraphic framework ("imperfect sketches of the Geology"). The imperfections, with other considerations, may have influenced him not to publish the memo which rendered subsequent publications less clear and less useful than had the memo been published. Darwin recognised the influence of glaciation on the Permian sedimentary rocks in the area but did not publish his observations and interpretatio

Revised terminology of the Late Cambrian - Ordovician sequence of the Florentine - Denison Range area, and the significance of the "Junee Group"

The area of Lewis's original "Junee Series" is unsuitable as a basis for definitive stratigraphy and correlation,even with units in adjacent areas. A review of the various usages and concepts associated with the "Junee Group" indicates considerable diversity in meaning and application of the term, and suggests that the sequences are better considered in terms of a lower clastic unit and an upper limestone unit rather than as a single group. Accordingly, the Late Cambrian-Ordovician sequence in the Florentine Synclinorium is defined in terms of the Denison Subgroup, comprising four formations between the basal unconformity on the Denison Range and the base of the limestone, and the Gordon Subgroup, comprising three limestone formations and the Westfield Beds. These two Subgroups together approximate to the "Junee Group"