Geological notes on the countrytraversed by the Derwent Valleyrailway extension.(incl.plate xiii.).

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The great basaltic sheet, once continuous from Macquarie Plains to Glenora, ends somewhat abruptly on the Northern slope of the valley of the River Styx.Whether it originally extended farther is uncertain, but the probability is that its advance was barred by thick bedded tertiary sands and clays corresponding to those exposed in the bed of the Derwent near Macquarie Plains, and covered in pre-basaltic times by a great accumulation of drift gravels, the greater part of the whole formation being subsequently removed by denudation.Half a mile from the Glenora station the new line passes through solid basalt, the continuity of which is broken by an irregular band, the determination of the character of which will require a more careful examination than is practicable on a flying visit. It is loosely compacted, and some of it has the appearance of volcanic tuff. But the interesting feature is that, scattered through the formation are crystalline patches of opal varying in colour from pure w

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