17G VOLCANIC KOCKS OP SOUTH-EASTERN QUEENSLAND 



along tlie railway cuttings, between Harlaxton and Spring 

 Bluff. It is well bedded, loosely aggregated, and in a very 

 weathered condition. 



In the Municipal Quarries at Toowoomba, distinct 

 evidence of central vents is present, and it is in this district 

 only that evidence of prolonged and important extrusions 

 of basic material from eruptions of the central type is 

 found. 



Chemical Composition. 

 The analysis of the oligoclase-basalt from Spicer's 

 Peak is seen to be very similar to the mugearite analysis. 

 It is richer in silica and poorer in ferric oxide, but the 

 lime, magnesia, total alkalies, titania and phosphorus 

 pentoxide are very similar. The Spicer's Peak rock is 

 poorer in soda but correspondingly richer in potash. There 

 is a close similarity between the basalt from Cooper's 

 Plains and the lower basalt in portion 69 at Chinghee Creek. 

 This similarity is interesting as the Cooper's Plains basalt 

 represents one of the most recent flows of the area, and the 

 Chinghee Creek flow one of the earliest, as it belongs to 

 the lower division. 



The basalts from Pittsworth and Mount Lindsay are 

 also very similar. Chemical distinctions cannot be made 

 between the rocks of the lower and upper divisions, nor 

 can they be distinguished microscopically. 



