784 GENERAL GEOLOGY OF MAHULAN AND TALLONG, N.S.W., 



some of which are very persistent along the line of strike. On 

 the flanks of Ballanya Hill there occurs a banded chert of very 

 striking appearance. It is composed of alternate bands of white, 

 and black colours; faulting and folding on a minute scale have 

 taken place, and many hand-specimens illustrate these structures 

 very beautifully. 



The formation, as a whole, is intensely folded and crumpled, 

 and all the more solid bands of rock show evidence of this action 

 in the development of slaty cleavage. The finer bands, however, 

 remain in the condition of shales. In these shales an abundant 

 and well preserved graptolite-fauna is developed. 



The lower levels of the great Shoal haven Gorge are composed 

 of highly contorted slates and quartzites. In spite of assiduous 

 search, no fossils have been discovered in this series. They are^ 

 however, very similar to the rocks in Limekiln Creek, a small 

 tributary entering the western bank of Barber's Creek, and in 

 this series graptolites have been found. The age of the Shoal- 

 haven beds is thus presumably Ordovician. Their folded char- 

 acter, as compared with the simple tilting of the Silurian beds, 

 is additional evidence of the same fact. 



Sihirian Rocks. 



Silurian rocks, definitely determinable as such, have a very 

 wide range in the district, while rocks presumably of that age 

 cover an even wider extent. Lying to the west of the Ordovician 

 belt, at its southern end, there is a well defined belt of limestones. 

 These extend from a point a little to the north of Hogg's Lime- 

 kilns, southward beyond Bungonia Caves. At this latter place, 

 they are exposed in a magnificent clifiF, 1,700 feet high, forming 

 the bank of Bungonia Creek. 



Their northerly extension is interrupted by the Glenrock 

 grano-diorite, which has cut them ofif there. As this eruptive 

 roek is later than Silurian, the limestones have suffered intense 

 metamorphism, and few traces of fossils are recognisable. At 

 the lime-kilns, however, distinct traces of coarse Favosites and of 

 Tryj)lasma show the age of the beds to be Silurian. Further 



