lf)2 PROCEEDINGS OF THE ROYAL SOCIETY OP QUEENSLAND. 



valley, one finds the How in question outcropping on the 

 road and in the paddocks on either side. The extent of the- 

 outcrop has not been determined, but it covers a consider- 

 able acreage, while the thickness is ijrobably something 

 more than 20 feet. 



The flow forms one of the most recent of a large 

 number which rest approximately horizontally upon the 

 denuded surface of the Bundamba Sandstones of Upper 

 Triassie age, and in all probability the flow was poured 

 out in Upper Kainozoic times. 



About one-half mile nearer to Mapleton than this 

 anorthoelase basalt one finds rhyolitic rocks outcropping 

 in a very weathered condition. In other parts of the 

 Blackall Range, e.g., near ]Montville and Flaxton, the 

 upper basalts have been poured out over the rhyolite, and 

 this is probably the relation of the different rocks at 

 ^lapleton. Immediately underlying the anorthoelase 

 basalt flow is a considerable thickness of olivine basalt, 

 which is well shown in the section over Avhich passes the 

 water at Baroon or ]Mapleton Falls. 



The height above sea-level is approximately 1.400 feet, 

 and both to the south and west the range falls away 

 steeply. 



Generally speaking the basalts of the Blackall Range 

 are very much weathered, and considerable depths of soil 

 are accumulated on the surface. This rock yields a very 

 ric-h nd soil, and the weathered surface has a distinctive 

 dark-brown colour which serves as a useful indication of 

 its weathered outcrop. 



In collecting specimens, the extreme toughness of the 

 rock is evident and in marked contrast to most of the 

 basalts of the area. For purposes of road construction this 

 toughness should result in a resistance to abrasion superior 

 to that of the other basalts in the neighbourhood, and as 

 such it has a special value. 



MEGASCOPIC CHARACTERS. 



In general grain-size and colour the basalt is quite 

 normal, but the presence of numerous phenocrysts of more 

 or less lozenge-shaped anorthoelase felspars is a charac- 

 teristic feature. An occasional phenoeryst, lath-shaped and 



