THE VICTORIAN NATURALIST. 87 



areas of the Thomson and the Tanjil. These two streams, for 

 the first few miles of their courses, have a generally westerly 

 direction ; they then turn sharply, the Thomson to the north and 

 the Tanjil to the south. The explanation, based on their peculiar 

 courses and the character of the country in that region, appears 

 to be that the Thomson has captured the north branch of the 

 Yarra and the Tanjil the south branch. The main mass of Baw 

 Baw consists of a massif of grano-diorite that has been intruded 

 into a vast area of Ordovician and Silurian slates and sandstones, 

 which have a generally northerly strike. This has caused the 

 induration of these sediments for some distance back from the 

 contact. The result has been to prevent the east and west 

 streams from cutting through this mass as quickly as the north 

 and south streams, which run along the strike of the strata, and 

 probably along a great fault line. In consequence the Thomson, 

 cutting its way south, and the Tanjil north, were more quickly 

 able to corrode their channels than the Yarra was able to cut its 

 way E.S.E. across the beds. Baw Baw was shown to be a 

 plateau with a general altitude of about 4,800 feet. The 

 whitened remnants of myriads of dead Snow Gums attest the 

 former occurrence of a stunted forest, killed probably by 

 boring insects rather than by bush fires. The Yarra Falls, 

 six in number, 700 feet in aggregate height, as ascertained by 

 Messrs, Walker and Campbell, have hitherto been considered 

 unique, but Mr. 15aragwanath's survey has shown that all the 

 streams flowing north, east, and south-east form similar falls, 

 some of them 1,000 feet, near the grano-diorite contact, while 

 those flowing south have a uniform though rapid descent to 

 the much less elevated region, covered with Cainozoic sediments 

 and volcanic deposits. 



The paper was illustrated by lantern views of district maps and 

 photos, of the Upper Yarra and Falls, kindly lent by Mr. A. J. 

 Campbell, and of Walhalla-Baw Baw district by Mr. Barnes, 

 of Walhalla, together with those of the Walhalla-Tyers district by 

 Mr. Kitson. By their aid the topography as hitherto known, and 

 as modified by Mr. Baragwanath's survey, was clearly shown. 



In the discussion which followed, Mr. C. R. Ford mentioned 

 that on the island of South Trinidad, in the South Atlantic, he 

 had noticed a patch of hundreds of dead trees which apparently 

 had been destroyed simultaneously. Many speculations were 

 made as to the cause of their destruction, but all the theories 

 put forward failed to throw any light upon the subject. The 

 agency of a wood-boring larva was suggested as the cause, but 

 the examination of a considerable number of trees did not reveal 

 any signs of their former presence, 



Mr. D. Le Souef, C.M.Z.S., said that whilst in Western 

 Australia he had noticed that the larvse of beetles attacked only 



