no 
The South Australian Naturalist. 
the order of activity was:-— 1. Aii explosive outburst from the 
Mount Gambier crater; 2, a brief effusive phase at the same 
focus; 3, renewed ex])losive activity at that crater; 4, explosive 
eruption of Blue Lake crater; 5, explosive eruption at Leg of 
Mutton crater. Stillj there is no positive evidence against the 
idea that pluises 3, 4. and 5 were contemporaneous. 
The Blue Lake is the most remarkable and most fascinating 
of the subsided areas. The average depth of the water is 
250 ft. to 280 ft., the height of the cliffs averages 250 ft. above 
the water, and the cliff* faces are \evy steep. The shape of the 
lake is an irregular oval, and the area is 170 acres. As already 
mentioned, the Avater of the lakes is portion of that stored in 
the great sub-artesian tertiary basin of the ancient Murray 
Gulf, and tlie surface of the lakes sloAvly rises and falls, iji 
liarmony with the rise and fall of the general Avater-table of the 
whole area. 
When the rainfall affecting this area is from 18 to 20 
inches per annum, the level of Avater in the lakes remains prac- 
tically stationary. From this it may be deduced that the 
amount of Avater that is added to the underground supply from 
an annual rainfall of 18 to 20 inches is just about equal to the 
loss of Avater from the great underground reservoir per annum. 
This loss is due mainly to the outlets along the southern coast- 
line, Avhere it constantly gushes forth in great quantities. 
If Ave regard the underground reservoir of the south- 
easterji district as a closed system with an annual overflow 
equal to the average annual increment of Avater received from 
an annual rainfall of 18 to 20 inches, then aa^c may construct 
a graph to shoAv the reiatioji betAveen the rainfall and the rise 
or fall of level in the Blue Lake. 
