BY H. I. JENSEN. 567 



regard to the Narrabri-Dubbo line was practically the reverse of 

 what it was in the Carboniferous, the sea being then to the west 

 and the land to the east. The New England late Palaeozoic sea 

 was, however, of very considerable depth, as evidenced by its 

 limestones and radiolarian beds, but the Mesozoic seas of Central 

 Australia and of the Gunnedah Basin in particular, were only of 

 slight depth, and may be looked upon as mere transgressions. 



The Permo-Carboniferous of the Gunnedah Basin has, in the 

 Warrumbungle region, a sharp south-east dip; the overlying 

 Trias-Jura is almost horizontal, having but a slight north-west 

 dip. Consequently earth-movements of some amplitude must 

 have taken place between the Permo-Carboniferous and the Trias- 

 Jura, but there is no evidence of intense folding since the Car- 

 boniferous. In the Nandewars, where the Permo-Carboniferous 

 strata are well exposed, the sharp dips are due to faults, the 

 folding movements in the sediments having produced only gentle 

 dips. It is different in the southern end of the Nandewar 

 Mountains, at Maule's Creek; here the folding connected with 

 the epeirogenetic uplift of New England has been very much 

 more intense, and was accompanied by fractures through which 

 rhyolitic lavas were extruded. The faulting in the Bullawa 

 Creek area is much later and connected with the alkaline 

 intrusions. 



In the Warrumbungle Mountains we meet with a complete 

 series of alkaline lavas, ranging from very acid to very basic. 



The order of eruption was the following : — 



1. Comendite, pantellarite, and arfvedsonite trachyte erupted 

 first as tuffs into cones of which the pasty lavas were often 

 squeezed as a plug. Flows occurred in the central part of the 

 volcanic district where activity was most intense. 



2. Nosean, pseudoleucite segirine, and arfvedsonite phonolites 

 as plugs and flows. 



3. Phonolitic segirine trachyte and alkaline andesites (kerato- 

 phyres and lahnporphyry), as vast flows, probably from fissures. 



4. Alkaline basalts and trachydolerites. 



