•278 FOSSILIFEROUS TUFF, ETC., AT CAVAN, 



All the above are thickly distributed in the shales, and one is 

 reminded of the Hume beds(2) at Hatton's Corner where the same 

 species are to be found; so that there can be no doubt as to the 

 Glenbower formation being of the same age, that is. Upper 

 Silurian. 



As Mr. R. Etheridge, junr., in writing about Barrandella 

 Imgui/era, Sby., var. wUkinsoni, and Cyathophyllum shearshyi, 

 mentions(3) that these two fossils, together with Rhizophyllum 

 inter punctatiim, De Kon., are so characteristic of the Hatton's 

 Corner shale that the name of either may be selected as a designa- 

 tion for that bed; but as the Rhizophyllum is also found in a 

 lower bed of the section, he prefers to call the bed the " Barran- 

 della Shale"; the occurrence of both the Cyathophyllum and the 

 Barrandella in the shale at Cavan should, then, prove a very 

 close relationship between the Hatton's Corner and Glenbower 

 beds. 



The width of this exposed strip of Upper Silurian strata is not 

 more than about fifteen chains, for it is overlaid on the west and 

 south-west by the mass of igneous rocks consisting of a dark 

 coarse tufaceous rock resembling quartz porphyry near the Glen- 

 bower anticline, and, lower down towards Clear Hill, of felspar 

 porphyries, felsite and rhyolite. The felspar porphyries are of 

 two colours, one of a dark chocolate, and the other of a beautiful 

 green, each with crystals of pink felspar embedded in the base. 

 The felsites are also of a similar green colour, probably owing to 

 the presence of chlorite. All these rocks take a high polish. 



These lavas and tuffs rise to a height of about from 300 to 500 

 feet above the level of the river in the near vicinity, but farther 

 south they form grand and imposing hills known as the Murrum- 

 bidt^ee Mountains, from which extensive views of the Yass- 

 Murrumbidgee district can be obtained. 



Knowing that some attempts had been made to trace the 

 junction of the Silurian and Devonian rocks of the Yass district, 

 I was of the opinion, after overhauling the fossils contained in 

 the Glenbower deposits, that I was in close proximity to the 

 required spot. I knew I could not be far from Devonian rocks, 



