142 R. A. WEARNE AND W. G. WOOLNOUGH. 



V. Geology -(I) Sedimentary Rocks. 



(a) Per mo-Carboniferous Rocks. — An inlier of Permo- 

 Oarboniferous rocks is to be found immediately to the north- 

 west of Mount Barney, a high double peaked mountain, 

 which is situated about six miles to the north-north-west 

 of Mount Lindsay. These rocks have been previously con- 

 sidered as of Trias-Jura age, but the discovery of a definite 

 specimen of Fenestella fossula, Lonsd., submitted to Mr. 

 W. S. Dun for identification places them in the Permo- 

 Oarboniferous. This is the first record of Permo-Oarboni- 

 ferous fossils in the West Moreton District. 



(b) Trias-Jura Rocks. — The representatives of the Trias- 

 Jura rocks met with in the area under consideration are 

 to be referred to the Welloon stage. They consist of con- 

 glomerates, grits, sandstones, and shales with thin seams 

 of coal. The coal measures form rather poor soil, and the 

 surface ridges are mostly used for grazing purposes. 



(II) Eruptive Rocks. 

 Four distinct periods of volcanic eruption can be traced 

 in the West Moreton District by the occurrence of : — 



1. Trachytes. 



2. Andesites and Dacites. 



3. Rhyolites. 



4. Basalts. 



1. Trachytes. 

 Trachyte eruptions occurred along a zone running from 

 the main range to Mount Oordeaux in an easterly direction 

 to Redbank Plains, about eight miles south-east of Ipswich. 

 These eruptions produced a number of cones, whose denuded 

 remnants may now be seen at the summits of the main 

 range and at Mounts Matheson, Greville, Edwards, French, 

 Flinders, and the ridge to the south of Redbank Plains. 

 The flow of this period attained a thickness of about 2,000 

 feet. 



