1872.] DAHirxKEE — geology or qtjeenslajStd. 313 



and along the Carpentaria -watershed.. The vast Cretaceous and Oolitic 

 tracts lying to the westward of this line would seem to be entirely be- 

 yond their limit of action. 



YoiCANIC. 



Whilst the older Trappean rocTcs have apparently had so much 

 influence on the disturbance and fracture of the sedimentary strata 

 older than the Carboniferous, and by a secondary process have evi- 

 dently been centres of mineralizing action, the volcanic seem to have 

 played the most important part in determining the elevation and 

 present physical outline of North-eastern Queensland. 



As will be seen by reference to the Map (PI. IX.),the main outbursts 

 of lava have taken place along the dividing range which separates 

 the eastern and western waters, and therefore on the line of the 

 highest elevation of the country. 



The more northern volcanic areas, those shown on the Map north 

 of latitude 21°, are probably contemporaneous with the " upper vol- 

 canic " series of Victorian geologists, so extensively developed in the 

 western districts of that colony. These have issued from well-defined 

 craters still in existence, and are probably of Pliocene Tertiary age. 



The southern areas, viz. Peak and Darling Downs &c., are older, 

 agreeing with the " lower volcanic " of Victoria, which have been 

 ejected through fissures, and have in no case a very extensive flow, 

 beyond the Hues of fracture through which they issued. These may 

 be referred to the Miocene Tertiary epoch (PI. XII. figs. 1 & 2). 



The rock-masses forming both the " upper " and " lower " volcanic 

 are basic in character, and may, with rare exceptions, be all grouped 

 under the general term " dolerites." 



Mr. Allport's description of a typical specimen from the Clarke 

 river, with minor modifications, wiU hold good for most of the vol- 

 canic rocks of Northern Queensland (PI. XII. fig. 3). 



He says : — " This dolerite contains a triclinic felspar, augite, 

 magnetite, pseudomorphs after olivine. The felspar prisms are clear 

 and transparent, and exhibit well the striae and bands of colour when 

 examined in polarized Hght. The augite occurs in small brown 

 crystals and grains ; it frequently contains black magnetite, and is 

 sometimes slightly altered. The olivine has been completely altered 

 to iron oxide, and appears in the sections as bright red grains and 

 crystals. Pseudomorphs of quite similar character occur in the do- 

 lerites and basalts of the coast of Antrim." 



After the examination of several specimens from various localities, 

 he adds : — " These are characteristic felspathic dolerites, and contain 

 neither nepheline nor leucite." 



The single exception that came under my observation in the upper 

 volcanic was that of an interstratified bed of a highly siliceous rock, 

 in which nearly one half the mass was composed of quartz crystals 

 arranged in a quartzose matrix. 



The " lower volcanic " are, as a rule, far more altered and decom- 

 posed than the upper, and assume more the amygdaloidal character, 

 the usual occupants of the cavities being zeolites or calc-spar. 



VOL. XXVril. PAET I, Z 



