BY H. C. RICHARDS. 115 



all probability there was a connection between the Tam- 

 borine PlateaiT and ^lacPherson 's Range, and also a general 

 extension in a westerly direction to Mount Lindsay. The 

 length of time over which the volcanic activity resulting 

 in these deposits extended must have been considerable, for 

 in many cases the formation of soil on the surface of the 

 tlows has taken place, and in others river gravels and 

 lacustrine deposits have been formed before the succeeding 

 iiow has been poured out. 



There seems to have been a decided lapse of time be- 

 tween the extrusion of the lower and middle divisions of 

 rocks, for in the Lamington area the acid agglomerate 

 belonging to the middle division rests on extremely 

 weathered basaltic material, and incorporated in the acid 

 agglomerate are lumps of underlying soil. The same holds 

 good between the middle and upper divisions. 



In the Upper Chinghee Creek area, a deposit of river 

 gravel several feet thick, containing w^ell-rounded pebbles 

 of the underlying basalts and rhyolites, occurs between the 

 rhyolite and the overlying basalts. The upper division is 

 made up of a large number of flows, and there are abundant 

 instances in many localities of the production of surface 

 soils before the succeeding flow took place. In some cases 

 there are stems and roots associated with the soil, and in 

 other places deposits of diatomaceous earth, between suc- 

 cessive flows of lava, as at Mount ^Meerschaum, Beech 

 Mountain. Point Danger, &c. 



The total amount of denudation which has gone on 

 since volcanic activity ceased has been very large, and 

 valleys have been carved out to a depth of 2,500 feet— e.g., 

 the Christmas Creek Valley — through the volcanic rocks. 

 In other places, as in Canungra Valley, there has been a 

 cutting down through 1,000 feet of volcanic rocks, and 

 through 700 feet of Mesozoic sediments, giving to-day a 

 stream with a very meandering nature. At Cunningham's 

 Gap also, the volcanic rocks had been denuded at least 1,500 

 feet, giving a well-rounded valley before the faulting 

 along a north and south direction, which resulted in the 

 so-called air-gap, took place. It is thus quite clear that 



