520 J. T. Jiitson: 



In 1907 Mr. A. M. Howitt (11) reported briefly on some reefs 

 at Warrandyte, and noted a fossiliferous locality, and a basic 

 dyke. 



The Silupian Rocks of the District generally. 



(a) Area. 



With the exception of the older basalt at the Kangaroo 

 Ground and some tertiary gravels, silurian rocks occupy the 

 whole of the country here dealt with. 



(b) Petrology. 



The rocks of the district show little variation in lithological 

 character. They consist mainly of shales with sandstones of 

 varying degrees of coarseness. The shales are perhaps the most 

 predominant. Throughout wide areas they are thick-bedded 

 and massively jointed, as well as extremely rubbly. Bands of 

 sandstone, generally from 3 to 12 inches thick, are sparsely 

 interbedded with them. Occasionally sandstone bands up to 6 

 or 8 feet in thickness are met with ; but they, as well as con- 

 tinuous sections of the same rock, are rare. Mica (generally 

 muscovite) is extremely common in both the shales and sand- 

 stones, but in the latter rocks the flakes are larger, and there- 

 fore more noticeable. Many of the shaly rocks are when unde- 

 composed, moderately tough, but on exposure they soon soften 

 and break up. 



The sandstones have been so silicified in places as almost 

 to have become quartzites. Almost the only rocks that can be 

 called quartzites occur in a narrow band of rocks running from 

 the " Kopje," through Burt's Hill, and along the western side 

 of Brushy Creek. Silicification has occurred all along this line, 

 but only in parts have true quartzites been produced. The 

 grains of the rocks in this band are finer than in. most sand- 

 stones elsewhere met with. Slates are almost wholly absent 

 from the district. 



In the immediate neighbourhood of Warrandyte, conglome- 

 rates, grits and coarse sandstones are associated with the shales. 

 The coarse-grained rocks outcrop oh the ridges and slopes, par- 



