THE SOUTHERN COAL FIELD TABLELAND BASALTS. 247 



The sill ends up abruptly at the fault, and the volcanic 

 material has been forced along the plane for a few feet. 

 Minor faulting leading to displacement of under two feet 

 followed, and finally further volcanic activity led to the 

 sill being intersected by several dykes. 



The geological phenomena which have been mentioned 

 appear to have occurred in the following order: — 



1. Deposition of fossiliferous sediments, late Tertiary age. 



2. Uplift, Transition period. 



3. Faulting, Post Tertiary age. 



4. Intrusion of sills and dykes, Post Tertiary age. 



5. Further slight faulting, Post Tertiary age. 



6. Intrusion of later dykes, Post Tertiary age. 



The tectonic forces indicated must have occupied a con- 

 siderable time, for the uplift was gradual, otherwise very 

 heavy faulting would have taken place. Such is not the 

 case, however, for the maximum amount of displacement 

 by any individual fault is only about 230 feet, as agaiust an 

 uplift of 2,000 feet. 



It is recognised that no great lapse of time was necessary 

 for the four latter phenomena to have taken place, but it 

 was by no means abrupt. The very fact of the uplift indi- 

 cates a change of epoch, and it is thought that the evidence 

 points to the dykes and sills having been injected during 

 Pleistocene epoch. 



Chemical and petrographical work indicate a marked 

 affinity between the dykes and sills and the basalts found 

 capping the tableland areas, and a common magma basin 

 and period of vulcanicity is evidenced. 



No vents were found from which the surface basalts 

 could have emanated, and it is thought that they represent 

 a portion of the volcanic product which welled over the 

 earth's surface from fissures induced by the uplift. 



