10(} VOLCANIC ROCKS OF SOUTH-EASTERN QUEENSLAND 



the age of the volcanic activity, and the field occurrences 

 of the rocks in a few of the localities have been described. 

 Dr. H. I. Jensen has thoroughly dealt with the alkaline 

 representatives, and as a result they have gained a rather 

 undue prominence, for it is found that they form quite a 

 minor portion of the extensive development of volcanic 

 rocks in the area. 



The calcic or sub-alkaline rocks have received scant 

 attention, and microscopic and chemical investigations have 

 been, with the exception of the Main Range district, 

 restricted almost entirely to the alkaline rocks. 



The area under investigation covers about 4,000 scjuare 

 miles, and is in the extreme south-eastern corner of Queens- 

 land. It is bounded by the Pacific Coast on the east, by 

 MacPherson's Range on the south, by the Main Range on 

 the south-west and west, and on the north by an east and 

 west line from Toowoomba to the coast. In addition to 

 this main area, the strip of country between the coast and 

 the D'Aguilar Range as far north as the Glass House 

 Mountains, and the Brisbane River Valley as far north as 

 Esk, are added. 



During the last five years the author has travelled 

 extensively over this area, more particularly, however, in 

 the southern portion which is the least known geologically. 

 All the important localities have been investigated. Alto- 

 gether twenty-five complete analyses^ of volcanic rocks of 

 this area have been recently made in the laboratory of the 

 Agricultural Chemist, and these analyses, together with 

 nine published by Dr. Jensen,- furnish analyses of all the 

 important rocks. Thus it is possible to enter upon a corre- 

 lation of the various types on chemical lines. 



Owing to the abs(mce of any important development 

 of fossiliferous rocks since late Mesozoic times, physio- 

 graphical considerations must be availed of in elucidating 

 the Cainozoic history of this area. 



The physical features are so largely connected with 

 the origin and structures of the volcanic rocks that an 



^Ann. Kept. Agric. Chem., Q 'land, 1912, 191.3, 1914. 

 :Proc. Linn. Soc, N.S.W., xxxi.-xxxiv. (190(31909). 



