194 PROCEEDINGS OF SECTION C. 



2.— SUMMARY OF WORK ON THE ALKALINE ERUPTIVES OF S.E. 



QUEENSLAND. 



By R. A. WEARNE. 



Research work on the alkaline eruptives was carried on in the 

 following areas : — 



1. Main Dividing Range, near Cunningham's Gap. 



Mt. Matheson (2660 ft.) was found to be the main focus of 

 the trachyte eruptions of this district. It is composed of 

 trachyte very similar in character to the comendite of Jensen from 

 Mt. Edwards, surrounded by tuffs and huge masses of trachyte 

 agglomerate. 



Mts. Spicer & Mitchell (4000 ft.) The section exposed on 

 the escarpment of Mts. Spicer and Mitchell was found to consist of 

 alkahne trachyte, tuffs and breccia for a thickness of 1500 ft. sur- 

 mounted by 1000 feet of olivine basalt. 



_ 2. Mt. Alford (2200 ft.), about 7 miles to the east of the 

 Main Range, was found to consist of andesites and quartz- 

 diabases, intruded by rhyohte dykes. 



Glennie's Pulpit, on the north-western front of Mt. Alford, 

 was found to be the plug of a rhyohte centre of eruption which 

 intrudes the andesites of that mountain. 



3. Mt. Greville (2700 ft.) was found to consist of grorudite 

 intruded by decomposed basalt dykes, 



4. Mt. Maroon (3300 ft.) was found to consist of rhyolite 



5. Mt. Barney (4300 ft.) was found to consist of rhyohte 

 intruded by basalt and dolerite. 



Volcanic Sequence. 



The volcanic sequence was found to be — 



1. Trachytes. 



2. Andesites and Dacites. 



3. Rhyolites. 



4. Basalts. 



(1) Andesite intrudes trachyte at the Main Range. 



(2) Rhyolite intrudes trachyte at the Main Range, near Cun- 



ningham's Gap. 



(3) Rhyohte intrudes andesite at Mt. Alford. 



(4) Basalt intrudes rhyohte at Mt. Barney. 



Age of Eruptions. 



The age of the volcanic eruptions was found to be Trias-Jura 

 contemporaneous with the uppermost portion of the Walloon 

 stage of the Ipswich coal measures. 



Proofs. — (1) Water-worn trachyte pebbles were found im- 

 bedded in Trias-Jura conglomerate of the Walloon stage at Laidley 

 Valley and Mt. Flinders. (2) Volcanic tuff containing Trias- Jura 

 plant imprints (Taeniopteris Daintreei) was found associated with 

 basalt at the " Hip Roof," a meridional razor-back between the 

 Little Liverpool Range and the Main Range, near Toowoomba, 



