28 THE GLASSHOUSE -MOUNTAINS 
The last part of Mr. Stutchbury’s statement should 
have given him the clue to the formation of these remarkable 
mountains. He tried to account for their formation as 
masses of plutonic rocks, as igneous rocks which had 
crystallized at depths, and failed. If he had tried to account 
for them as volcanic rocks, he would have been more 
successful. He recognized that “there were as many foci 
of heat as there are now mountains,’ but he went no farther. 
The simplest explanation of their origin is that each marks 
the site of a volcano, once standing as a truncated cone, 
its sides built up of alternate layers of tuff and lava, and 
having a crater at its blunt apex. Below the crater and 
piercing the central axis of the mountain was the pipe 
up which molten matter made its exit at each volcanic 
outburst. After the last explosion, this pipe was filled 
with a plug of solidified lava that formed the hardest rock 
of the mountain. By denudation through successive 
ages all the softer parts of these volcanoes have been swept 
away. Theslopes of tuff, or volcanic ash, and lava have gone, 
the crater has gone; except in the case of Crookneck or 
Coonowrin nothing is left but the plug of volcanic rock 
which filled the volcanic vent. Even this is now suffering 
denudation in turn. Round the base of each mountain 
is a talus of blocks, detached from its surface by the action 
of frost, running water and the daily variations of temper- 
ature. With one exception, they rise baldly from the coast 
plain on. which they stand. This exception is Crookneck, 
which has as its base a small collar of Trias-Jura rocks. 
The continuous rains of the first quarter of 1893 brought 
about an immense landship on Crookneck, and the booming 
and rumbling of the rock slide caused some alarm in the 
neighbourhood ; the fissure produced by the fall of this 
immense mass is plainly visible on its 8.E. side. 
In 1875, the late Sir Augustus Gregory, in his report on 
“The Geology of Parts of the Wide Bay and Burnett 
Districts,” classes the Glasshouse Mountains with Mounts 
Cordeaux and Mitchell and Spicer’s Peak in the Main Range; 
and with Mount Lindsay and Mount Barney in the Mac- 
pherson Range. He calls the rock in each case a porphyry, 
and says, “The porphyry consists of a pale brown paste 
with minute felspathic crystals, though it sometimes varies 
