578 THE DISTRIBUTION, ETC., OF ALKALINE ROCKS, 



direction. From this fracture a number of east and west cross- 

 fractures originated, and volcanic activity was displaced from 

 west to east along them, just as the modern volcanoes of Fonseca 

 Bay are displaced from east to west. The explanation which, in 

 my paper on this district, I advance to account for the dip of the 

 Trias-Jura fails if Suess' theories are correct. The easterly dip 

 of the Trias-Jura in the monocline of the N. D'Aguilar and 

 Blackall Ranges can be explained just as well by assuming, as 

 probably Suess would do, that the early Tertiary push was 

 exercised in the same sense as that of the Palaeozoic folding, viz., 

 from west to east. Then the long fault along which the lavas 

 were extruded borders a portion of the subsided Vorland. The 

 monocline is then due just to a bending of the strata before sub- 

 sidence. The Woondoom Tableland to the north of Cooran is 

 undoubtedly, as I have shown in my paper, a horst bordered by 

 faults. 



The main fracture (the volcanic line) has always Palaeozoic 

 rocks near it to the west, and has universally Trias-Jura strata 

 to the east. It is therefore situated along the margin of Mesozoic 

 sedimentation, and it was probably formed in early Tertiary time 

 by the subsidence of the Trias-Jura area which was probably 

 land in the late Cretaceous. The horizontality of most of the 

 Trias-Jura beds everywhere except in the mountain-range shows 

 that they can only have been subjected to vertical movements. 



Much of the Mesozoic strait which connected the Ipswich and 

 Burrum Coal Measures is now resubmerged under the waters of 

 Moreton Bay. After all, the nature of the Ipswich and Burrum 

 Beds shows that the Trias-Jura sea was only what Suess would 

 term a mere "transgression." The islands in and around Moreton 

 Bay are to my mind the product of subaerial erosion in late Cre- 

 taceous times, prior to the early Tertiary downthrow The present 

 tendency in Moreton Bay is distinctly towards elevation. 



The volcanic line in the ocean about 100 miles east of Brisbane, 

 which runs parallel with the Glass Mountain fracture, may mark 

 the eastern rim of the Triassic sea. If the Bowen Coal Measures 

 occur under the Trias-Jura here, the analogy of the situation of 



