BY JOHN SHIRLEY. B. SC. 31 
and the prevailing winds. Ngungun is weathering most 
rapidly from the south, Coonowrin from the south-west, 
Beerwah from the north, and Toonbubudla from the north- 
west. Toonbubudla and Beerburrum seem to weather 
almost equally towards all points of the compass. 
The columnar structure may best be studied in the 
caves at the foot of the column on Coonowrin. Though 
they are usually six-sided, there are exceptions to the rule 
in four and-five-sided prisms. 
The most porphyritic rocks are those of Beerburrum 
and Ngungun. The formerly usually weathers a rich red- 
brown. Specimens from Beerwah and Beerburrum have 
been classified by Mr. Jensen as Trachyte; those from 
Coonowrin, Tibrogargan and Ewan as Comendite; and 
those from Ngungun as Pantellarite, a soda trachyte in 
which the percentage of silica ranges from 66.8 to 72.5, 
and alkalies, principally soda, amount to 10 p.c. 
The heights of the principal peaks are :—Beerwah, 
1760 feet ; Coonowrin, 1170; Toonbubudla, 1020; all the 
others are below 1000 feet. 
The Glasshouses arise from Trias-Jura beds, while 
immediately to the west of them are rocks of Carboniferous 
age. With regard to the age in which they were formed, 
all that we can say is that they are more recent than the 
Trias-Jura, and older than the surrounding basalts. 
