BY H. I. JENSEN. 579 



the Glass Mountains and New South Wales alkaline rocks would 

 be very close. 



We have seen that the Glass House Mountains are situated on 

 the fractured border of a Palaeozoic land-mass, that the Mesozoic 

 sediments east of them are the product of the Trias-Jura trans- 

 gression, that although the folding of Trias-Jura sediments has 

 occurred to a limited extent, faulting and fracturing have played 

 a more important part in shaping this area in Post-Triassic times. 

 In all respects we find the correspondence with other Australian 

 alkaline areas very great. 



In discussing the Warrumbungles and Nandewars I did not 

 make any reference to the existence of cross-fractuies. 



An examination of my special papers on these regions shows 

 that in the Warrumbungles the main fracture runs N.N.E., and 

 there seems to be a tendency for cross-fractures to develop at 

 right-angles to this line. 



In the Nandewars the main fracture runs N.N.W., and a 

 number of minor fractures originate in it and run at right-angles 

 to it. Here the displacement of activity seems to have been from 

 east to west, that is from the land-side towards the inland sea. 



Further north in Queensland, continuing along the margin of 

 the Burrum Beds, we have syenitic masses of Post-Triassic age, 

 such as Mt. Boppy, examined by Mr. B. Dunstan, F.G.S. 



Mr L. C. Ball informs me that to the west of Gladstone there 

 are more trachytes essentially similar in character and mode of 

 occurrence to the Glass House. Further north, at Yeppoon, we 

 have another group, a specimen of which in my collection does 

 not possess the alkaline facies. All these Queensland trachytes 

 take the form of steep-sided cones or monoliths of columnar rock, 

 which represent plugs in tufl'-cones now removed by denudation, 

 and mamelons. 



More trachytic knobs occur in the Clermont district. These, 

 like the Yeppoon ones, have never been geologically examined, so 

 all that can be said is that they too stand on the rim of Mesozoic 

 basins. 



