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



and French. These he assigns to a variety of alkaline 

 lavas. He is of opinion that " the volcanic rocks of the 

 Fassifern Scrub are all Post-Triassic and probably Post- 

 Cretaceous." He describes the area under consideration 

 as a senkungsfeid and gives a detailed account of the 

 tectonic geology. 



Marks 1 is of opinion that the age of the volcanic series 

 in the neighbourhood of Beaudesert is Trias-Jura, in which 

 idea he follows Rands. 2 



In an account of Mount Lindsay in the Macpherson Range 

 Andrews 3 describes the eruptive trachytes as Trias-Jura 

 in age. 



It will be seen then that considerable diversity of opinion 

 exists in connection with this important question. 



Ill, Physiography.— The contour of the Main Dividing 

 Range which separates West More ton from the Darling 

 Downs reveals the fact that two successive uplifts occurred, 

 the first an uplift of about 2,000 feet, and the second of 

 about 2,700 feet. The summits of the Main Range — Mounts 

 Castle (3,700 feet), Cordeaux (4,100 feet), Mitchell (4,000 

 feet), Spicer (4,100 feet), Huntley (4,150 feet), Roberts 

 (4,350 feet), and Wilson (4,060 feet) are practically at a 

 uniform height above sea level. They represent the 

 denuded remnants of an uplifted peneplain. The uniform 

 level of this uplifted peneplain can* be seen from the summit 

 of Mounts Spicer and Mitchell gently sloping westwards 

 across the Darling Downs. 



Four well defined "air gaps " occur between Spring Bluff 

 and Bald Mountain, Mounts Cordeaux and Mitchell, Mounts 



1 Marks, E. S. — Coal Measures of South East Moreton, Queensland 

 Geol. Survey, Publ. No. 225, p. 52, Brisbane 1910. 



2 Rands, W. H.— Eeport on the Albert and Logan District, Qeensland, 

 Pari. Papers. C.A. 5, p 2, Brisbane, 1889. 



3 Andrews, E. C. — A Preliminary Note on the Structure of Mount 

 Lindsay. Rec. Geol. Surv. N.S.W., Vol, vn, 1903, pp. 328 - 240. 



