106 PROCEEDINGS OF SECTION C. 



23. (a) Stonier, G. A. : Ann. Rep. Dept. Mines, N.S.W., 1892, 127 p. ; (b) 1894, pp. 131-137; 



(c) 1895, p. 168. 



24. Suess, E. : " The Face of the Earth," Vol. IV., p. 561, ei. seqq. 



25. Suess, E. : Ibid, Vol. Ill, p. 236-262 ; Vol IV., 305-314, and authorities there cited. 



26. Thiele, E. O. : " On the Dolodrook Serpentine Area and the Mount Wellington Rhyolites, North 



Gippsland," Proc. Roy. Soc. Vict., Vol. XXV., 1908, p. 249. 



27. Twelvetrees, W. H. : " Outlines of the Geology of Tasmania," Proc. Roy. Tas., 1900-1901, p. 62. 



28. Twelvetrees, W. H. : " Outlines of the Geology of Tasmania." 



29. Twelvetrees, W. H. : Rep. Dept. Lamis and Surveys, 1909, p. 26, 29, map. 



30. " Report on the Mineral Resources of the Districts of Beaconsfield and Salisbury," 1903, p. 3. 



31. " Gunn's Plains, Alma, and other Mining Fields of the N.W. Coast," Bulletin No. 3, Geol. Sur. 



Tas., 1909, p. 5. 



32. Gunn's and Petterd, W. F.: " Some Igneous Rocks from the Heazlewood District," Proc. Roy. 



Soc. Tas., 1897. 



33. Waller, G. A. : " Report on the Zeehan Silver- Lead Mining Field," 1904, p. 10. 



34. Ward, L. K. : " Tin Fields of North Dundas," Geol. Sur. Tas., Bulletin No. 6, p. 30. 



35. Wilkinson, C. S. : Ann. Rep. Dept. .Mines, N.S.W., 1885. 



Plate II. 

 Geographical Sketch Map ot the Nuxdle District. 



3.— THE GEOLOGY OF THE YASS DISTRICT. 

 By A. J. SHEARSBY, F.R.M.S. 



Plates III. 



The area under consideration embraces the country traversed by 

 the Southern Raihvay from Gunning on the east to Bowning on the 

 west, a distance of about 26 miles, with a -breadth of about 12 

 miles. As it is mostly of a mountainous nature, it presents great 

 difficulties to the geologist who single-handed attempts to solve 

 the problems with which the district abounds. 



The country at Gunning consists of shales highly folded and 

 faulted by intrusions of quartz porphyry and granite. These shales 

 are apparently barren of fossil remains. Their relation to the other 

 sedimentary beds to the west points to them being Upper Silurian, 

 probably a little older than the Bango and Yass Beds. 



To the west of Gunning the country passed over is chiefly 

 granite, to about the 173 mile peg, two miles on the Yass side of 

 Oolong railway platform. This granite decomposes into a very 

 fertile soil. Many imposing perched blocks of denudation are to 

 be seen from the railway line near the 170 mile peg. 



At the 173 mile peg the granite gives way to about eight miles 

 of shales, mudstones, and quartz beds, most of which are of a very 

 barren nature, both as regards plant food and fossils. For eight 

 miles the train travels over these sedimentary beds, the Jerrawa 

 Shales. They are folded and contorted so much that the same beds 

 are continually being exposed, forming an isoclinal fold. 



At about 18^ miles the Jerrawa shales are replaced by quartz 

 porphyry. Near the 183 mile peg it will be noticed that the 

 porph3n"y is distinctly columnar. 



At Coolalie (184 miles) the country is more or less level, and 

 the bed rock is covered by recent deposits, so that no change is 

 observable from the railway. The beds here are, however, silurian 

 sediments, consisting of limestone, shales and sandstones, and are 

 best studied a mile or so to the north near Bango homestead — the 

 Bango Beds. Towards Yass the cuttings show quartz porphyry 

 similar to that last mentioned, and would lead one to believe that 



