April, 1936. The Queensland Naturalist 
105 
the world. In plan they are almost perfectly circular, 
while in elevation they appear as evenly sloping cones 
truncated at the top. On comparing pictures of several 
of those conical volcanic peaks you may notice that 
some have considerably steeper flanks than others. This 
variation in slope is very significant and most informa- 
tive, for the slope of each is determined by what the 
engineer terms the angle of repose of the ejected 
material, which in turn depends upon the coarseness 
of this material. In those instances where the erupted 
fragments have been relatively large the cones may slope 
at angles as high as 40 degrees, but where the volcano 
is made up mostly of small fragments the slopes of its 
side are correspondingly gentle. If one were to climb 
to the top of one of these cones of volcanic ash one would 
find a depression or crater shaped like a funnel with its 
walls sloping at just the same angle as the outer slopes 
of that particular mountain. 
In addition to those volcanic mountains that are 
built up entirely of fragmental material violently thrown 
into the air, we have others that are formed by succes- 
sive flows of hot liquid lava more or less quietly poured 
from a central vent. These, too, tend to form cone-shaped 
mountains but they are usually less symetrical than the 
cinder cones as the lava sometimes wells over one side of 
the crater’s lip and sometimes over another. The shape 
that the mountain ultimately attains will vary, too, with 
the chemical nature of the lava. Basaltic lavas are so 
fluid that they flow long distances from the centre of 
eruption before cooling into solid rock, in this way 
building up mountains covering large areas with very 
gentle slopes. At the other extreme are those acid lavas 
rich in silicia, which are so sticky and viscous that they 
are unable to flow very far from the vent and, conse- 
quently, build up very tall and steep volcanoes. Inter- 
esting examples of the former type of mountain are 
found in the volcanoes of Hawaii. Mauna Loa, the 
greatest of these, rises 14,000 feet above the sea, but 
measured from the ocean floor, from which it has been 
built, it is over 30,000 feet high. Its diameter at sea 
level is eighty, miles and its base covers many thousands 
of square miles of the ocean floor. The crater of this 
giant volcano is three miles in diameter and 1,000 feet 
deep. But in spite of its enormous size, this mountain 
is not at all impressive as viewed from afar. This is due 
to its very gentle slopes, which vary from only three 
degrees to eight degrees and which are a true indication 
of the liquidity and hence of the chemical composition 
of the lava. Contrast with this giant but almost flat 
