104 
The Queensland Naturalist April, 1936. 
the not so distant past. In his famous Geological Map 
of Queensland, published in 1892, Dr. R. L. Jack shows 
about fifty '‘Volcanic Foci” and others have been dis- 
covered since that date. Probably the best known of 
these recent volcanoes are represented by the crater lakes 
of Barrine and Eacham in the north and the Coalstoun 
Lakes in the south. 
Perhaps before we proceed any further, we should 
decide what we mean by a volcano. Dr. Johnson in his 
famous dictionary defined a volcano as a “burning 
mountain.” Such a definition is simple and graphic and 
lias met with wide acceptance, but it is not literally true. 
Volcanoes do not burn in the ordinary sense that a fire 
burns and, moreover, they are not necessarily mountains, 
for while to a geographer a volcano is a hill, to a geologist 
it is a hole. Here is a modern definition of a volcano 
in the geological sense: “A volcano is a channel through 
the outer solid crust of the earth, communicating with 
a portion of the heated interior, through which hot 
gases, molten lava and fragments of rock pass upwards 
to the surface. The eruptive activity may take place 
quietly or with exploisve violence ; it may be continuous 
or spasmodic. It may or may not give rise to a moun- 
tain of accumulation around the orifice of ejection.” 
Since they combine in themselves phenomena of 
purely academic interest with matters of more intimately 
human concern, volcanoes have always received the close 
attention of intelligent travellers and students,, so that 
a great number of valuable observations of their habits 
have been recorded from many parts of the world. In 
recent years, these observations have received notable 
additions from the modern observatories which (adequately 
equipped for thorough and continuous study) have been 
established on Vesuvius and Etna in the Mediterranean, 
on Kilauea in Hawaii and in Java. 
One result of the vast amount of research that has 
been done on the subject is to show that volcanic activity 
exhibits itself in so many ways that it is unlikely that 
one simple explanation will account for every manifes- 
tation in all its details. 
Some volcanoes are produced by a series of under- 
ground explosions hurling dust, ashes and rock frag- 
ments through an orifice vertically into the air. These 
drop down as showers immediately about the crater. As 
one eruption succeeds another, there is built up first a 
mound, then a hill, and finally a mountain perhaps 
thousands of feet in height. In this way are formed 
some of the Tnost beautifully symmetrical mountains in 
