BY A. J. SIIEARSBY. 28 < 



Nowhere, in fact, have I observed sedimentary strata among the 

 fragmentary beds of the Snowy River porphyries." However, a 

 footnote on the same page reads as follows : — " Since these notes 

 have been in the press, I have examined a most interesting 

 series of sections observable in traversing the country from the 

 W Tree, near Murendel Hill, eastward to the Butcher's Creek. 

 I found here that the Snowy River Porphyries consist of beds 

 over a thousand feet in thickness, of the usual fragmental char- 

 acter, with interbedded sheets of felstone, whose lower surfaces 

 when visible are scoriaceous and conformable to the inequalities 

 of the underlying strata. Here, however, for almost the first 

 time, I notice that some of the beds have a marked conglomerate 

 character, and nearly all of them include numerous fragments of 

 slates and sandstones (quartzites) of the character of the Lower 

 Silurian of the district. ''(8) 



This note cleared away the difference, for, as I mentioned 

 before, I have found in the Yass porphyries, which rest upon the 

 Silurian rocks, very many pieces of shale and limestone whicli 

 contained fairly well preserved fossils of the Silurian period. 



The foregoing interesting comparisons strengthen my opinion 

 as to the age of the main mass of the volcanic rocks in the Yass 

 district, and I further believe that I am right in looking upon 

 them as part of the Snowy River Porphyries. Macroscopically, 

 the Yass rocks are identical with those of Victoria, and it would 

 be difficult to differentiate between those belonging to each 

 district in a mixed collection of rocks from both localities. 



It will therefore l)e seen that a detailed study of the volcanic 

 rocks of Yass will be most interesting and instructive. The 

 localities where they occur are most accessible, being close to well 

 made roads, a point in their favour which I am informed is not 

 possessed by the localities in Victoria where the Snowy Kiver 

 Porphyries abound. 



They are also worth investigation from a commercial point of 

 view, on account of the numerous traces of galena and copper 

 which occur in many places among these rocks, and which so far 

 have not received much attention at the hands of the local 

 people. 



