182 



year at which the chief eruptions took place. These efforts 

 were not attended with any positive results, but it will be 

 seen from fig. 4 that the average graph of the winds for the 

 year corresponds, roughly, with the outline of the limits of 

 the finer volcanic material, and confirms the idea that the 

 ash distribution was governed by winds similar in direction 

 and velocity to those of the present day. 



East winds are very rare throughout the whole year, 

 which fact corresponds with the limited distribution of the 

 ash to the west of the craters. South-easterlies are com- 

 monest in late January and February, while north-west and 

 west winds are strongest in September and October. The 

 graph of the average' October winds corresponds most closely 

 with the actual distribution of the ash. The chief point of 

 discordance is that the extent of the ash deposits to the 

 south, towards O.B. Flat, etc., is greater than the average 

 amount of north wind would suggest. 



The question of the duration of vulcanicity is discussed 

 later, but if it be fair to assume that the wind circulation was 

 at that time much as it is at present, as suggested ' by the 

 graph, and if it be further shown that the duration of the 

 volcanoes' life was brief, then the foregoing results suggest 

 that the explosive activity took place about the middle of 

 the later half of the year. 



6. Age of the Eruption. 



(a) Relation to Victorian Newer Basalt Period. — Before 

 discussing the age of the Mount Gambier vulcanicity it is desir- 

 able that its relationship should be established with the great 

 period of eruptive and effusive vulcanicity that occurred in 



Railways 



Fig. 5. 



Sketch map showing the area covered by Newer Basalts. 



in South-western Victoria, and the volcanic localities of 



South-eastern South Australia. 



