78 Proceedings of the Royal Society of Victoj'ia. 



Thickness of the Strata. — Sir Alfred Selwyn* gives a section, 

 before noted, passing through Mounts Alexander and Tarren- 

 gower, and on the evidence of this, states that the thickness of 

 the Silurian rocks of this district is not less than 35,000 feet. To 

 get this thickness on this line of section, and with the average 

 dip he gives, no allowance can be made for repetition by folding, 

 I cannot find that he ever gave reasons for altering his opinion 

 on this point, but we find him in 1861 (Ex. Ess., p. 177), and 

 again in 1866 (Ex. Ess., p. 11), applying these figures to the 

 whole of the upper and lower silurian rocks combined. This, his 

 more recent statement, has been generally followed and quoted. 

 Now the west end of the silurian trough of his section is nearly 

 on the strike of the Chewton anticline, where it runs into the 

 granite ; so that perhnps he could have calculated the true 

 thickness of the Castlemaine series along his section line, though, 

 from the indications of a northerly pitch, I do not think so. 

 Since the days when Selwyn made this traverse of a dilficult and 

 practically unexplored country, and without suitable maps, great 

 changes have taken place. Railway and road cuttings, water- 

 races and mines have given facilities, that he was without, for 

 examining the rocks. 



The lowest beds, as shown by the presence of T. fruticosus, 

 crop out near the west end of tlie Elphinstone tunnel, so that we 

 have here an anticline, which, though auriferous west of Taradale, 

 at Drummond and Lauriston, some miles to the south, is very 

 poor in quartz- reefs, and apparently non-auriferous at this locality. 

 A slight syncline occurs to the west, at about the meridian 

 of the seventy-fourth mile post on the railway line, though the 

 highest zones are missing. The crest of the next great anticline 

 I'uns, as before stated, through Chewton. Selwyn places the main 

 syncline between Castlemaine and Maldon, about Muckleford 

 Creek. Taking this last observation of his as correct, we can 

 calculate the thickness approximately. From the Eureka Reef, 

 where an outcrop of the T. fruticosus zone occurs, to the west 

 end of John o'Groat's Gully I have plotted all the anticlines and 

 synclines I could detect. Jn this distance (two and one-eighth 

 miles) I find : — 



» Pari. Rep., loe. cit., ami Q.J.G.S., vol. x. 



