90 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



ley, Joadja creek and Wollongong at the south and Murrurundi 

 (Doughboy hollow) at the north. The only important deposit in 

 the Lower Coal Measures is at Greta near Newcastle in northeast 

 port of the province. 



Long ago, Clarke®'* recognized the close resemblance of this 

 mineral to the boghead or Torbanite of Scotland. He thought it 

 due to local decomposition of some resinous wood and believed that 

 the lens-form of the deposits and their passage laterally into shale 

 could be explained easily by supposing the mineral to be due to 

 drifted resinous trees, undergoing changes in shallow pools sur- 

 rounded by material changing into ordinary coal. The quartzose 

 constituents are merely sand carried by wind into the pool. The 

 thickness of the deposit depended only on the supply of drift timber. 



Wilkinson"" says that the kerosene shale occurs in irregular 

 lenses, sometimes in actual contact with layers of coal as at Joadja 

 creek, sometimes wholly unassociated with layers of coal, as at 

 Hartley, or even as forming part of a great coal bed, as at Greta. 

 At the last locality, the boghead is a great lens in the coal, but there 

 are many petty lenses of the same material scattered through the 

 coal benches. At Joadja, one finds small irregular patches of bright 

 jet-like material, plant remains lying horizontally and numerous 

 vertical stems of J\vtcbraria. whose lustrous bright jet substance is 

 in contrast with the dull luster of the shale. 



David''^ found the shale in one place at the bottom of a great 

 coal bed; Mackenzie''- found it at the top in another; while in still 

 another David found a mass of alternating coal, clay and " shale," 

 five beds of the boghead and four of bituminous coal. xAt the last 

 locality the whole mass thinned out in one direction, the several 

 layers disappearing in succession until the last layer of boghead 

 passed into bituminous shale. There he saw many stems of Verte- 

 braria, both vertical and i)rostrate; in one tunnel, some of them four 



*" VV. B. Clarke, "Mines and Mineral Statistics of New Soutli Wales," 

 Sydney, 1875, pp. 17^-180. 



'^ C. S. Wilkinson, " ]\Iines and Min. Stat., 1875," p. 131; Ann. Rep. Dept. 

 Mines, 1884, pp. 149, 156; i8go, p. 208. 



"T. W. E. David, Ann. Rep. Dept. Mines, 1888, p. 170: 1890, pp. 221-224; 

 1892, pp. 159-163. 



"-J. Alackenzie, Rep. 1895, p. 104. 



90 



