126 VOLCANIC ROCKS OP SOUTH-EASTERN QUEENSLAND 



As E. 0. Marks and R. A. Wearne, the most recent 

 writers on the age of the volcanic activity resulting in these 

 rocks, have so definitely advocated a Trias-Jura age for 

 at least a considerable portion of them, the author has 

 found it necessary to deal with this matter rather fully. 

 Marks writes^* : — 



" The present writer in examining the coal- 

 measures south of Brisbane came to the conclusion 

 that the volcanic rocks met with, almost entirely of 

 the basaltic type, belong to two ages, Trias-Jura and 

 late or post-Tertiary. In a fiying visit to the coal- 

 seams outcropping on the Upper Logan district, a 

 site was pointed out by Mr. Buchanan, where an out- 

 crop of carbonaceous shale or weathered coal had 

 been covered by a recent slip in the bank of Christ- 

 mas Creek. Mr. Buchanan remarked on the outcrop 

 being perpendicular, and the writer observed that 

 the sandstone in juxtaposition with the fallen 

 ground was also perpendicular, and that this sand- 

 stone contained rounded pebbles of basalt similar 

 macroscopically to the andesitic basalt of the neigh- 

 bourhood. Some distance further down the creek, 

 a similar sandstone is seen resting on the basalt. 

 Owing to circumstances, a detailed examination 

 could not be made then, but the section thoroughly 

 convinced the writer of the Trias-Jura age of the 

 basalt in that locality. . . . The sandstone and 

 included basalt is presumably on the same horizon 

 as that observed by Mr. Rands, and ascribed by 

 him to the Desert Sandstone. ... It is more 

 than probable, there being no evidence to the 

 contrary, that the sandstone observed by Mir. Rands 

 is of Trias-Jura age, like the remainder of the 

 sandstone in the neighbourhood." 



It was the above that mainly led Marks to a Trias- 

 Jura age for most of the basaltic rock, more especially 

 for that in the eastern portion of MacPherson's Range. 

 The cliff section pointed out by Mr. Marks was the one 

 already described by the author earlier in this paper (see 



"Proc. Roy. Soc, Q'land, xxiii., pt. 2, p. 142. ■ 



