282 FOSSILIFEROUS TUFF, ETC., AT CAVAN, 



further prospecting will probably prove the existence of more 

 payable lodes. 



At the Devil's Pass the rocks, which are similar to those at 

 Nutter's Mountain, are piled up to a great height, and the views 

 from this look-out are magnificent. 



I do not know how far this volcanic belt extends to the south- 

 west from this point before the Devonian limestones are met 

 with : it is not far I believe, but to the north-east a distance of 

 three and a half miles has to be covered before one meets at the 

 Horseshoe Bend, on the Yass River, the Upper Silurian shales 

 and limestones. At this point the sedimentary rocks are very 

 highly inclined, and strike in a north-westerly direction. They 

 underlie the same strange porphyritic tuff which is met with in the 

 Glenbower anticline, but at this point there is an enormous body 

 of it, for nearly the whole of the country between the Horseshoe 

 Bend and the Devil's Pass is composed of it. 



This peculiar rock is of a dark grey colour, and containing, as 

 it does, coarse blebs of quartz, together with felspar and mica, 

 has been diagnosed by some as a quartz porphyry; but as it 

 occurs in places showing distinct bedding, and, above all, in 

 several parts of the district it contains unaltered fragments of 

 limestone and shale with fossils, I think it must be put down as 

 a tuff highly metamorphosed and silicitied. 



This will then account for the occurrence of the beds of 

 *' Fossiliferous Granite," as it has been called, which I have come 

 across at Murrumbateman and Oak Range, both places near 

 Yass. At these localities may be seen large masses of this rock, 

 which, if broken open, will be found to contain, scattered through 

 the mass, fragments of limestone and shale, with corals and 

 brachiopods, which show in some cases signs of weathering, but 

 no trace of alteration by heat. One specimen of this tuff obtained 

 at Oak Range, a few miles north of Yass, contains a very good 

 cast of the columnal of a Crinoid, Cyathocrinus (?), and another 

 the pygidium of the trilobite, Encrlnurus, in a matrix of lime- 

 stone, showing that these tuffs were laid down after the forma- 

 tion of the Upper Silurian rocks. 



