BY H. C. RICHARDS. 123 



locality is there any interbedding of the volcanic flows or 

 pyroclastic material with the Mesozoic sediments, but on 

 the other hand there is abundant evidence of inclusions of 

 the Mesozoic sediments in the overlying volcanic rocks, 

 ilhyolitic pitchstone, trachytic and basaltic dykes and sills 

 intrude the Walloon Coal Measures in different localities. 



In several places, deposits of diatomaceous earth a 

 few feet thick occur between successive tlows of basalt in 

 the upper division of volcanic roks. These deposits occur 

 at Mount Meerschaum, Beech Mountain, Tweed Heads, near 

 Rosewood &c. In some cases the diatomaceous material has 

 been altered into common opal,^'' but where it is unaltered 

 frequent traces of plant-remai?is are found. These remains 

 are imperfectly preserved and not capable of precise deter- 

 mination, but am.ongst them remains of dicotyledonous 

 plants can be recognised ; this places these basaltic flows as 

 post-Trias-Jura at least. In the middle division of acid 

 -and sub-acid rocks abundant fragments of the Mesozoic 

 sediments occur. The most notable example is in a 

 small cliff section in Upper Christmas Creek, between 

 portions 62v and 72v. Here, a mass of shale many feet in 

 diameter is included in volcanic agglomerate. The shale 

 is standing with its bedding approximately vertical and it 

 contains not only a highly carbonaceous band, but also 

 fossiliferous shale bands containing Cladophlehis which 

 characterises the Upper Trias-Jura measures of this 

 locality. 



.An examination of this section leaves no doubt what- 

 ever as to the included nature of the mass of shale, and it 

 furnishes definite evidence of a post-Walloon age for this 

 volcanic material. The compactness and nature of the 

 material in the shale-block indicate that a considerable 

 period of time had elapsed between its formation and the 

 ■disruption from the bedded position. 



The basalts of Cooper's Plains and the trachytic 

 material at Redbank Plains both overlie the Oxley beds 

 as shown by ^Marks'" and Cameron. The Oxley beds which 



'" Q'land Mineral Index, Q'land Geol. Surv., Pub. 241, p. 961; 

 E. W. Skeats, Proe. Eoy. Soc, Q'land, xxvi. (1914). 



'' Q'land Geol. Surv., Pub. 225 (1910), p. 53. 



