BY H. C. RICHARDS. 175 



The basalt at Cut Hill near Coolangatta is very 

 similar indeed to this rock. 



Specimen 237.— Quarries, Bundamba. This repre- 

 sents one of the most recent flows in the whole of the area, 

 and is largely quarried for road-making purposes. 



It is a compact non-porphyritic basalt, and under the 

 microscope it is seen to be holocrystalline. The brown 

 glass which is studded with rod-shaped crystals of iron-ore 

 is not very abundant. {See Plate XIV., fig. 4.) The 

 rock is rather coarse in texture, the plagioclase laths aver- 

 aging 0-6 mm. in length, and the augite which occurs in 

 ophitic patches well developed may extend to 1-5 mm. in 

 length. 



Olivine is abundant, and occurs in rounded crystals 

 up to 1 mm. in diameter. The plagioclase is an acid 

 labradorite. 



This rock is certainly a flow, and it shows ophitic 

 structure better developed than in any other rock examined. 

 Specific gravity 2-92. Name : Basalt. 



Basaltic Tuffs and Agglomerates. 



These do not occur to any great extent, and are really 

 of very limited occurrence. At Christmas Creek, betweec 

 Lamington and Lamington Glen, basaltic agglomerate 

 which is made up of rounded boulders and scoriaceous frag- 

 ments occurs immediately beneath the acid agglomerates 

 of the area. There is no great thickness and it represents 

 the surface of the lower basic rocks. The surface material 

 at Spicer's Peak, on its extreme eastern end, is also 

 agglomeratic in nature, and represents in that locality the 

 most recent material which is preserved, of the upper divi- 

 sion of the basic rocks. It is probable that the explosive 

 element resulting in the agglomerate developed here and 

 also at Christmas Creek when the fissures which had 

 served as the extruding channels became choked up. 



Near Toowoomba there are very large accumulations 

 of basaltic tufi^, and numerous sections through it are seen 



