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ON THE OCCURRENCE OF A BED OF FOSSILIFEROUS 

 TUFF AND LAVAS BETWEEN THE SILURIAN 

 AND MIDDLE DEVONIAN AT CAVAN, YASS; 

 SIMILAR IN AGE AND CHARACTER TO THE 

 SNOWY RIVER PORPHYRIES OF VICTORIA. 



By a. J. Shearsby. 



(Communicated by W. S. Dun). 



(Plate ix.) 



The Parish of Cavan should in the future be of intense interest 

 to the geologist, as it shows rocks of the Upper Silurian age, 

 which until quite recently had not been observed in that district, 

 appearing as a conspicuous outcrop from beneath a bed of por- 

 phyries, tuffs and lavas which forms a distinct line of demarca- 

 tion separating them from a formation of more recent age, of 

 which the main portion of the Cavan beds are composed. 



The Cavan beds have in many instances been termed Siluro- 

 Devonian, but they will probably receive a more definite name 

 after a careful geological survey is made of the north-eastern 

 portion of the Parish, and the southern portions of the Parishes 

 of Boambolo and Waroo. 



The Parish of Cavan is about twelve miles to the south of the 

 town of Yass, and is bounded on the north by the Murrumbidgee 

 River, which in this part of the country pursues an exceedingly 

 tortuous course on account of the many obstacles in the shape of 

 the rugged hills of limestone and igneous rocks, which cause the 

 river to twist about, and add such a picturesqueness to the land- 

 scape. The district is essentially a pastoral one, sheep and cattle 

 doing remarkably well on the rich succulent grasses which abound 

 on all sides. The limestone ridges, however, require plenty of 

 rain, as although in spring they look much fresher and greener 

 than the adjoining hills, the warm sun of summer soon makes a 



