130 VOLCANIC ROCKS OP SOUTH-EASTERN QUEENSLAND 



(3.) Near Esk, one finds in the coal measures a great 

 amount of felspathic material in the shales and sandstones. 

 This is derived from the weathered grano-diorite which 

 occurs a few miles to the north-east, and an examination 

 shows all stages of the material, from thoroughly broken- 

 down particles right up to fresh grano-diorite pebbles-- 

 which are abundantly distributed through the beds. 



The felspathic particles in the shales are often quite 

 large, and bear a very close resemblance to the other 

 weathered felspars on the surface of the included pebbles. 

 The assumption that this material is trachytic tuff does 

 not seem at all justified, and the author interprets it merely 

 as felspathic sandstone and shale which are made up of 

 material largely derived from weathered grano-diorite. A 

 micro-section of the so-called "trachyte-tuff" which con- 

 tains fossil plants was shown to the author by Mr, Wearne 

 and it is best described as a fine-grained argillaceous sedi- 

 ment through which are distributed abundant angular 

 grains of quartz. There is nothing of the microscopic 

 characters of a tuff associated with this rock, and it bears 

 no resemblance to the undoubted tuffs which are found in 

 other parts of the area. 



(4.) This occurrence of trachytic material is between 

 portions 155 and 157, parish of Esk, and is encountered on 

 the roadside as one ascends the ridge towards Ottaba 

 Station from Esk. Instead of being alkaline trachyte inter- 

 bedded with shales, the author regards it as a dyke of 

 trachy-andesite. This material is very much weathered, 

 but a somewhat similar rock which has been analysed 

 occurs at portion 51, parish of Esk, and the latter is one of 

 the series of rocks which are regarded as belonging to an 

 intermediate series between the normal alkaline and sub- 

 alkaline series. The strike of the sedimentary rocks is 

 320° east of north, and of the dyke 340° east of north, and 

 the material cuts across the beds, so that it is a dyke and 

 not an interbedded flow. The strata are fairly highly 

 tilted here, and are made up largely of felspathic sand- 

 stones and shales, containing abundant Mesozoic plant- 

 remains. Quite close in the railway cutting, large dykes 

 of augite-andesite have definitely intruded and baked the 



