114 VOLCANIC ROCKS OF SOUTH-EASTERN QUEENSLAND 



Apart from the above instances, no important fault 

 movements are known to have occurred. 



Folding movements of only a very gentle nature have 

 taken place since the Palaeozoic era. 



The earth movements might then be regarded as being 

 of a vertical nature, and the important ones have taken 

 place in the western and north-western parts of the area, 

 along lines having a general north and south direction. 



These movements took place in Cainozoic time and 

 the last great movement occurred after the volcanic activity 

 had ceased for some time. 



V. VOLCANIC ROCKS. 



(i.) General Ppjtrology. 



The maximum thickness of volcanic rocks in any one 

 area is approximately 3,000 feet, and this is seen to be 

 made up in general of three m.ain divisions, the lower 

 basaltic members, the middle rhyolitic and trachytie mem- 

 bers, and the upper basaltic and andesitic members. The 

 upper division has the greatest development and the lower 

 division the least. 



This maximum thickness of 3,000 feet does not occur 

 only in isolated places, but is general along MacPherson's 

 Range, and in parts along the Main Range. The southern 

 plateaux have an average elevation of approximately 2,500 

 feet, with volcanic deposits about 2,000 feet thick. 



Tamborine Plateau, however, has an average thickness 

 of about 800 feet of volcanic rock; Springbrook Plateau 

 has about the same but rising to a thickness of 1,000 feet 

 at least at its southern termination. 



Lava flows exist at all levels from the sea-level at 

 Lytton, Wellington Point. Point Danger &c., to over 4,000 

 feet in the south and west. An examination of the map 

 shows that the present-day development is particularly in 

 the south and the west, but there is very strong evidence 

 of the development having been very much more extensive 

 both to the north and east of the present main masses. In 



