THE ESSENTIAL geology of the vast Australian continent was deciphered during the 19th century, by relatively few workers, often scholarly men of impressive intellectual and physical activity. To their study T. G. Vallance, very much of their ilk, naturally turned after his early creative surge of research in geology.
As a student and later staff member of the University of Sydney, Tom Vallance had researched on metamorphism - the alteration of rocks under pressure and temperature in the earth's crust. These studies led to the field of his most important contributions, on basalt, the black volcanic rock that flows from myriad volcanoes and constitutes the ocean floor. He was the first to realise fully that the weathering and alteration of such rock depends on its original eruptive state. Originally, crystalline basalt shows a very different pattern of alteration from chilled basalt glass, so that basalt of originally homogeneous chemistry but different physical state can alter to give rocks of strong chemical contrast. Such alteration affects not only the rock, but also the sea water circulating through it.
In making these crucial observations, Vallance laid the foundations for a lively field of science. This original work strongly influenced ocean-floor geology and the way in which workers viewed the mechanism of hydrothermal alteration during circulation of hot water in the ocean crust: his ideas received triumphant confirmation during the past decade after the development of submersibles had at last made detailed exploration of the sea-floor possible.
Before even this vindication Vallance's interests had begun to move into the historical field, especially with regard to the exploration of Australia. His work on geological expertise in Sydney during the late 18th and early 19th centuries shed unexpected light on scientific activity in the young colony and he held (and expressed) trenchant views on what he regarded as the successes and failures of Australian geology in the world scene. This work was recognised recently by the Sue Tyler Friedman Medal award of the Geological Society of London, which came when he was already aware that he was to die of cancer.
Tom Vallance was staunchly Australian and quietly proud of his descent from an early involuntary immigrant to New South Wales, but his many friends will remember him, with his courtesy and charm, as being as international as the science he studied, genially at home anywhere in civilised society.
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