BY H. C. RICHARDS. 117 



Apart from the fragmental material, however, very 

 extensive deposits of lavas of basic, intermediate and acid 

 natures occur. The most widespread distribution of lavas 

 is with the andesites and basalts belonging to the upper 

 division. 



lite lower division, made up of basic and sub-basic 

 rocks, is veiy widespread, being found over almost the 

 whole area in the south and south-west, which is at present 

 covered with volcanic rocks. The greatest development is 

 at Mount Lindsay where it has a thickness of at least 1,500 

 feet, but usually it is less than 100 feet thick. 



The middle division is made up of rhyolites and 

 trachytes together with their glassy and fragmental repre- 

 sentatives. As far as extensive development is concerned, 

 the rhyolites are confined to the southern portion extending 

 over an area bounded on the south by MacPherson 's Range, 

 while the trachytes occur in the south-west, generally along 

 the line of the I\Iain Kange. However, trachyte is found 

 in the southern area at Cainbable Creek, and rhyolite in 

 the south-western area at IMount Alford. A remarkable 

 similarity exists between the fragmental deposits all over 

 the southern area, and not only is this confined to the 

 actual nature of the material and its included fragments, 

 but also to the manner in which it occurs and weathers. 

 The acid lava is found either above or below the volcanic 

 agglomerate, though on the Springbrook Plateau, where 

 there is a widespread distribution of both lava and frag- 

 mental material, the lava occurs with agglomerate both 

 above and below. In the Main Kange area at Spicer's Gap, 

 the agglomeratic and tuffaceous trachytic material appears 

 to be above the trachytic lava. 



The thickness of this middle division may be 1,000 

 feet, as is the case at the Springbrook Plateau. At this 

 place the rock is rhyolitic and not more than 200 feet is 

 fragmental. 



The upper division, of sub-basic and basic rocks, is. 

 made up of a very large number of separate flows amongst 

 which, in the same locality, there may be considerable 

 variation. 



One may liave, as at Tamborine Plateau, fine-grained 



