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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 24, 



The exception occurs at Brisbane, where a dyke of quartz por- 

 phyrite cuts through, and is interstratified with, the Mesozoic strata 



Fig. 19. — Horizontal Cocd-Measures cut hy Trap-dyTces, Pelican 



Creek. 



there developed ; but its character is quite different from those of 

 Group 1. 



At Gladstone a dyke of the only true trachyte yet met with in 

 the colony is quarried for building-stone (PI. XL fig. 1). Its analysis 

 afforded me 



SiHca 67-800 



Alumina 14-666 



Perric oxide 5-350 



Potash 5-653 



Soda . 4-600 



Water, constitution 0-700 



Water, hygroscopic 0-600 



Specific gravity 2-320. 99-369 



This rock resembles the trachyte of the Puy-de-Dome. Crystals 

 of sanidin felspar occur in a crystalline felspathic base, the iron 

 being in finely disseminated scales of iron-glance throughout the mass. 

 No mineral veins occur in or near it. It traverses the Devonian 

 series of the district ; and although there is no proof of its relative 

 age, it has the appearance of a modern rock. 



The active influence of these trap disturbances of various periods 

 seems in Queensland to have been confined to the strip of country 

 lying about 200 miles back from, and parallel to, the eastern coast, 



