108 
The South Australian Naturalist. 
abundant. The value of these flints was appreciated by the 
aboriginals, ami not less so by the present inhabitants, for they 
are exported in considerable quantities. 
The surface of the underoToimd water is about 70 ft. to 80 ft. 
above sea-level at Mount Ganibier (140 ft. above sea-level), and 
is there ex])osed to view in a series of four beautiful lakes. 
The immediate neighbourhood of Mount Gambier might best 
be described by reference to the sketch given in fig. 1, which 
has been drawn in part from an aerial photograph taken by 
Mr. Arthur, of Mount Gambier, looking eastward. 
The present-day Mount Gambier is but a remnant of what 
was at one time a considerable pile of volcanic material, mainly 
fragmentary. A series of extensive collapses took i)lace along 
the line of the cones, so that the higher portions have almost 
wholly disappeared, and only the outer, lower slopes remain 
intact. The collapsed area is in part occupied by lakes, the 
surfaces of which are about 70 ft. below the level of the town 
and the surrounding ]dain. 
In the very early stages of the volcanic outburst there Wc4s 
a small flow of basaltic lava. This is exposed in section in the 
western and eastern wails of the Blue Lake, and in the eastern 
wall of the Valley Lake, with a thin deposit of volcanic ash 
sej>arating it from the underlying limestone. This lava is 
known locally as the “blue rock,’' in contradistinction to the 
beds of stratified tuff (ash), which are erroneously termed 
“lava.” 
