that there is considerable unconf ormability between tlie Upper 

 and Lower Silurian rocks of* Victoria, which would appear to 

 indicate that the Lower Silurian were subjected to consider- 

 able denudation, and to periods of plutonic activity before the 

 upper beds were laid down. Whether the regional metamor- 

 phism of the Mitta Mitta source basin is connected with 

 plutonic forces during Silurian times bj the lowering of the 

 area within the influences of central heat, which would re- 

 compose and crystallise the lower portions of the crumpled 

 Palaeozoic sediments, or are the "latest results of that general 

 process of transmutation, which all sedimentary deposits have 

 undergone and are still undergoing from the moment they 

 begin to be covered more or less thickly with other more re- 

 cent deposits," is still a matter of uncertainty. The re- 

 searches of Mr. Howitt* among the Devonian rocks of Gippsland 

 have unmistakeably shown that the close of the Silurian or 

 the beginning of the Devonian periods in the Australian Alps 

 was one of powerful volcanic activity, during which the 

 porphyries of Mount Cobberas and adjacent mountains were 

 laid down as accumulations of ash or tufa, subsequently con- 

 solidated ; and there is every probability that the intrusive 

 porphyries, which have invaded the metamorphic schists, are 

 connected with the volcanic and plutonic activity of that time. 



Deyo2^iak'. 

 The representatives of this system, crossed by the line of 

 section as at Coowambat and IS'ative Dog Creek, are indicated 

 by the fossils to be Middle Devonian, and as they are evidently 

 superior to the porphyries upon which they rest unconform- 

 ably, the latter may provisionally be classed as Lower 

 Devonian. The absence of Lower Devonian sediments is 

 noticeable — indeed, I am not aware that any such exist in 

 Victoria. The Middle Devonian formation is well developed 

 in the isolated patches of limestone at Bindi, on the Tambo 

 Eiver, and Buchan, on the Buchan Eiver, to the south from 

 the line of section. At both of these places an abundance of 

 its characteristic fossil, Spirifera levcecosta, may be collected ; 

 while at Mount Tambo, to the east of the Omeo Plains, bold 

 outcrops of purple conglomerates and sandstones are seen, 

 apparently stratigraphically superior to the marine limestones 

 at Bindi, and are regarded by Mr. Howitt as of Upper 

 Devonian age.* All these Devonian areas form now mere 

 pockets in the land surface, indicating vast periods of time, 

 during which the oscillations of the surface resulted — first, in 

 subsidence, during which they were laid down on the bed of 

 the ocean ; and, second, in emergence and folding, occasioned 



* " Devonian Kocks of Gippsland," A. BI. Howitt, F.G.S. 



