BY JOHN SHIRLEY, B. SC. 29 
so as to consist of very small grains of quartz with minute 
cavities, containing oxide of iron, resulting from the decom- 
position of pyrites. Occasionally, it is vesicular, and has 
the aspect of trachyte.”’ In speaking of the rock as con- 
sisting of a brown paste, Mr. Gregory must have had rocks 
of the Beerburrum type in view, and he very nearly gave 
their true composition when stating that they had the 
aspect of a trachyte. As a matter of fact, all these 
mountains are built up of forms of columnar trachyte 
in six-sided prisms. 
Leichhardt compared the Glasshouses to the Puys of 
Auvergne, a group of detached cones scattered over the 
centre of France, some of which still retain their cone-shaped 
slopes and central crater, while others have reached the 
state of denudation shown in our Glasshouses, and are 
reduced to the central plug of crystalline rock. The Puys 
are also columnar in structure, as may be seen in the illustra- 
tion handed round. 
A letter of Leichhardt’s, dated September, 1843, says : 
Last Saturday I returned from a trip to the Glasshouses ; 
the highest, Beerwah, is about 1,000* feet high, and is com- 
posed of a rock entirely different from the surrounding 
mountains; I have seen similar mountain features in 
Auvergne. Geologists have called this rock domite, 
because of its affecting the form of a dome. This domite 
belongs to the trachytic group. 
The Rev. J. E. Temison Wood believed the rocks of 
the Glasshouses to be basalt, and in his paper on the “ Desert 
Sandstone of the interior of Queensland,’ published plates 
showing ‘‘ Prismatic Basalt, Glass House Mountains.” 
Mr. Henry G. Stokes, formerly a member of this Society, 
was the first to show conclusively that the rocks of the 
xlasshouses belonged to the Trachyte class. Recently, 
Dr. H. I. Jensen, a Queenslander, and former resident of 
Caboolture, an ex-scholarship winner, and holder of 
a travelling science scholarship from Sydney University, 
has written two exhaustive papers for the Linnzan Society 
of New South Wales, in which the structure of the mountains, 
and the nature of their minerals have been fully discussed. 
* The true height is 1,760 feet. 
