406 W. K. BROWNE AND A. B. WALKOM. 



Rhacopteris tuff, Matthews' Gap Road. 

 Fine grained, very compact and laminated. It has a 

 bluish-grey colour when freshly fractured, but after short 

 exposure (a few weeks) to atmospheric weathering it 

 becomes brown. It has evidently undergone considerable 

 local movement, as seen from the large number of perfect 

 miniature faults which are present. It contains scanty 

 remains of Rhacopteris and Cardiopteris. 



Under the microscope it consists of rounded and angular 

 fragments of felspar and quartz, mostly very much iron 

 stained, cemented together by light-coloured glassy 

 material. A good deal of calcite is present. 



Cherty tuff, North of Mount Bright. 



Light-coloured greyish-green, fine-grained rock; lam- 

 inated and considerably jointed. Under the microscope it 

 is extremely fine-grained and is composed of minute grains 

 of quartz, and felspar and small amounts of magnetite and 

 probably rutile and pyroxene, with a cementing material 

 which appears felspathic. 



Summary. 



In the foregoing remarks we have endeavoured to 

 establish the following main points : — 



i. Partly underlain by earlier plutonic rocks, a complex 

 of Upper Carboniferous volcanic lavas exists in the Pokolbin 

 District constituting a series of inliers in the Permo-Oar- 

 boniferous sediments, the formation being substantially 

 continuous from a point about half a mile north of Drake's 

 Hill to the outcrop known as Jerusalem Rock. 



ii. A series of basaltic rocks occurs contemporaneous in 

 the Lower Marine of the Permo-Oarboniferous. 



iii. The two series of rocks together form a succession 

 showing a gradual order of differentiation from rhyolite to 



