248 



L. F. HARPER. 



A further point in favour of a Post Tertiary age being 

 assigned to the tableland basalts is their physiographic 

 disposition. In many instances they are found to have 

 accumulated over areas of country with drainage channels 

 corresponding in a marked degree with those of the present 

 day, thus indicating practically no topographic changes. 



Two instances of this feature may be cited. The follow- 

 ing section, published in the Iron Ore Deposits of New 

 South Wales, by Mr. J. B. Jaquet, Chief Inspector of Mines* 

 indicates the amount of erosion which had taken place in 

 the late Tertiary beds prior to the outpouring of the basalt. 

 It also shows how closely Post Tertiary drainage channels 

 agree with those of the present day. 



Wmgello District 



Tertiary 



Dsubun? ?000 ft above sea. level 



The second instance occurs in the valley of the Cordeaux 

 River, where the following section was obtained. 



Cordeaxix River 



M^KemblcL 



It will be noticed from this section how the basalt sheet 

 occupies slopes identical with those of the present day land 

 surface, and how an outlier of the Triassic rocks forms an 

 "island" now as it did at the time the basalt was outpoured. 



