GEOLOGICAL NOTES ON THE COUNTRY 

 TRAVERSED BY THE DERWENT VALLEY 

 RAILWAY EXTENSION. 



(PLATE XIII.) 



By T. Stephens, M.A., F.G.S. 



(Read November 8, 1909.) 



The great basaltic sheet, onoe continuous from Alac- 

 quarie 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 ac- 

 cumulation 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 white to dark brown. There are a'lso 

 faint but unmistakable traces of fossil wood. It was 

 from this same sheet of basalt that the fossil tree was 

 unearthed near Macquarie Plains, which was described' 

 by Sir Joseph Hooker some seventy years ago, and is 

 now a conspicuous object in the Natural History branch 

 of the British Museum. It has been identified by Mr. 

 Newell Arber as a species of Cupressinoxylon*. 



*Cupressinoxylon Hookeri. sp. nov., a silicified tree from, 

 Tasmania. By E. A. Newell Arber, M.A., F.L.S., F.G.S. Geo- 

 logical Magazine, January, 1904. 



