president's address. 565 



generation after generation undisturbedly lived and died ; while 

 the sands and gravel, now consolidated into sandstones, grits, and 

 conglomerates, bespeak ancient shorelines and sandbanks, where 

 littoral forms of life, such as Orthis, Cyrtodonta, Scolithus, and 

 various Trilobites, swarmed much in the same manner as the 

 cockle, lampshell, sandhopper, and lugworm upon our shores at 

 the present hour." 



Mr. Johnston evidently therefore considers the Lower Silurian 

 rocks of Tasmania of littoral origin, or as having been formed in 

 seas of moderate depth. 



(2) In Victoria the total aggregate thickness of the Upper and 

 Lower Silurian rocks has been estimated by Mr. A. K. C. Selwyn* 

 as 35,000 feet. 



Mr. R. A. F. Murray, F.G.S., the Government Geologist of 

 Victoria, has divided the Silurian strata of Victoria into the 

 following three groupsf : — (a) Metamorphic rocks and crystalline 

 schists, (h) Lower Silurian, (c) Upper Silurian. 



The first group probably represents altered Lower Silurian rocks 

 chiefly, but may include Cambrian and even Pre-Cambrian rocks. 

 It is chiefly developed (1) between the Wannon and Glenelg 

 Rivers near the west end of the Main Divide, and is in the 

 line of strike of the Archaean, Cambrian and Silurian rocks of the 

 west side of Tasmania, and (2) at the north-east end of the Main 

 Divide between the Ovens and Murray Rivers, on the line of 

 strike of the Archaean and Lower Silurian rocks of the east side 

 of Tasmania. 



The rocks consist of quartzites, granulite, foliated micaceous, 

 talcose, chloritic, and serpentinous schists, chiastolite schist, lep- 

 tynite schist, with garnets, hornblende schist, &c.| 



* Notes on the Physical Geography, Geology, and Mineralogy of Victoria, 

 by A. R. C. Selwyn and G. H. F. Ulrich, Intercolonial Exhibition Essays, 

 1866, p. 11. Melbourne, 1866. 



+ Victoria. Geology and Physical Geography, by Reginald A. F. Murray. 

 By authority. Melbourne, 1887. pp. 3.3-47. 



+ R. A. F. Murray, loc. cit. pp. 37-38, and A. W. Howitt, "Rocks of 

 Noyang," Trans. R. Soc. Victoria, xx. p. 18, and "Metamorphic Rocks of 

 the Omeo District, Gippsland," Austr. Assoc. Adv. of Science, Vol. i. 

 Sydney, 1887. pp. 206-222. 



