204 



itself is reserved for public purposes — Botanic, Forest, or 

 Public Park — and much has been done to add to the beauty 

 by planting and improvement, without destruction of the 

 unique natural features. 



The well-built nature of the town is largely due to the 

 abundant supplies of good building stones (limestones and 

 dolomites). The basalt is used for road making ( 22 J and the 

 ash forms excellent footpaths. The water supply is drawn 

 from the Blue Lake. But for the existence of the volcano, 

 the area would doubtless consist to-day of a broad limestone 

 plain, sparsely settled, and economically unimportant. 



11. Summary. 



1. The chief features of the previous literature of the 

 Mount Gambier area have been noted, and the main items of 

 its history described. 



2. The distribution of the volcanic ash has been mapped 

 and a contour plan of the Mount prepared. 



3. General conclusions regarding the course of the later 

 geological happenings have been arrived at, after a full dis- 

 cussion of the available evidence, as follows : ■ — 



4. Towards the end of the Newer Basalt period, at a 

 time little antedating the arrival of man, volcanic outbursts 

 occurred, subaerially, on the limestone plains of south-eastern 

 South Australia, associated with the very extensive outbursts 

 of Western and Central Victoria. 



5. A minor explosive phase was followed by the extru- 

 sion of a small lava flow. The main crater continued its 

 explosive activity and two other craters opened through the 

 lava flow along a line of crust al weakness. These eruptions 

 continued for perhaps two or three months, and then ceased, 

 having built up three cones to an average height of 650 ft., 

 and covered 25 square miles with ash deposits. 



6. Subsequently extensive collapse took place along the 

 line of volcanic activity, and practically the whole of the three 

 cinder cones caved in, forming great depressions, in the 

 deepest of which the waters of the sub-artesian basin formed 

 lakes. 



7. The origin of the water of the lakes is discussed, and 

 also the variation in the surface level, and suggestions are 

 put forward regarding the rate cf movement of the waters 

 in this important sub-artesian basin. The close correlation 

 between the annual rainfall and the variation in level of the 

 underground water supply has been graphically demonstrated. 



(22) This is brought from Mount Scliank ; the basalt at Mount 

 Grambier is quite inaccessible. 



