THE ALKALINE BOCKS COMMITTEE. 251 



The alkaline eruptives which are so conspicuous a feature of the 

 Fassifern and Esk Districts are entirely wanting in this district. 



Mount Whitestone, at the head of the Ma Ma Creek Valley, was 

 found to consist of Trias- Jura sandstone. 



(4) Fassifern District. — The following peaks off the Main Dividing 

 Range, which had not been inspected at the time of the last Congress 

 Report, were visited. 



Mount Castle, 3,700 feet, Mount Cordeaux, 4,100 feet, Mount 

 Huntley, 4,153 feet, and Mount Roberts, 4,350 feet, were found to 

 consist of alkaline trachyte capped by olivine basalt similar in character 

 to that of Mounts Mitchell and Spicer, and were probably built up by 

 the same volcanic flows. 



A remarkable, water-worn block of granite (quartz, orthoclase, 

 microcline, biotite, chlorite, apatite,, zircon, and decomposition pro- 

 ducts) was found near the source of Reynold's Creek, at the foot of 

 Mount Roberts. 



A careful search of the banks of the creek was made, as far as 

 practicable, but no trace of this rock could be found in situ. It is the 

 only example of a plutonic eruptive so far found in the district, and was 

 probably a xenolith. 



Mount Wilson, 4,060 feet, a conical peak at the junction of the 

 Main Range and the MacPherson Range, 60 miles to the south of Ipswich, 

 was visited twice. 



It consists of trachyte and basalt in the same sequence as that of 

 the more northern peaks, but the basalt is here capped conformably 

 by 400 feet of trachyte. This is the only mountain in the whole dis- 

 trict which shows this sequence. 



Mount Moon, 2,800 feet, an isolated peak about 8 miles to the 

 east of Spicer's Peak, consists of a very light alkaline trachyte very 

 similar to that of Mount Flinders, capping Trias-Jura coal measures. 



Mount Clunie, 3,500 feet high, a peak in the MacPherson Range, 

 to the east of Mount Wilson, consists of trachyte capped by olivine 

 basalt, which has assumed a perfect columnar structure. 



The second series of trachytes of Mount Wilson is wanting. 



The Twins, two small pyramidal peaks, about 6 miles to the east 

 of Cunningham's Gap, consist of alkaline trachyte capped by a remnant 

 of olivine basalt. 



Volcanic Sequence. 



The volcanic sequence was found to be — 



(1) Trachytes. 



(2) Basalts. 



(3) (a) Trachytes ; or- 

 (6) Andesites. 



(4) Rhyolites. 



(5) Basalts. 



