BY T. W. BDGEWORTH DAVID. 263 



with which last are associated the deposits of diatomaceous earth, 

 and a seam of lignite. It is not my intention here to attempt to 

 give a detailed description of that grand chain of trachytic 

 volcanoes, of which the Warrumbungle Mountains form a not 

 insignificant portion. Suffice it to say that they are the wrecks 

 of large volcanoes; and their cores of coarsely crystalline trachyte, 

 which have cooled deep down in the volcanic chimneys, now 

 rear themselves skywards as gigantic mo^ioliths, between 3,000 and 

 4,000 feet above the sea, and over 2,000 feet above the surrounding 

 plain, ringed round with alternating beds of coarse trachyte tuif 

 and lava. 



The chain extended probably from at least as far south as the 

 Canobolas, near Orange, northwards, perhaps, with intervals, to the 

 Glass- House Mountains on the coast north of Brisbane, a distance 

 of nearly 400 miles. As the diatomaceous earth deposits are 

 interstratified with the trachytes it is obvious that any evidence 

 which throws light upon the age of the trachytes has an equally 

 important beainng upon the question as to the age of the diato- 

 maceous earths. 



As shown on Plate xv., accompanying this paper, there is 

 clear evidence to show that the trachytes have intruded the 

 Pei"mo-Carboniferous Coal-measures in this neighbourhood. The 

 latter consist of sandstones, quartzites, cherts containing well 

 preserved specimens of Glossopteris, finely laminated black shales, 

 and at least one seam of coal, over 6 feet in thickness. The coal 

 has been calcined by the trachyte dykes, and at the extreme 

 right of the section, beds of trachyte tuff are -seen resting, with 

 strong uncomformity, on the Permo-Carboniferous strata. 

 Obviously then the eruption of the trachytes was later than Permo- 

 Carboniferous time. 



At several localities in the Warrumbungle Mountains the 

 trachyte series is seen to overlie sandstones, which are almost 

 certainly of Triassic age, and in this case the trachytes would be 

 proved to be Triassic or Post-Triassic. 



If now the chain of trachytic volcanoes be followed up into 

 Queensland, and traced north of the Glass-House Mountains, it 

 may be noted that near Port Mackay trachyte laAas and tuffs are 



