SOME GEO-PHYSICAL OBSERVATIONS AT BURRINJUCK. 457 



In an area such as that of Burrinjuck, where the earth's 

 crust has been proved to be fractured by many large faults, 

 there is not that strength of the crust postulated in Barrell's 

 investigations. Even small areas are divided in blocks by 

 fault planes, and it is conceivable that each small area may 

 work into a position of isostatic adjustment more or less 

 independently of its neighbour. Conditions such as these 

 would favour Hayford's limits for isostatic compensation 

 in areas of this type. 



If isostatic adjustment is not responsible for the deflec- 

 tions observed, are these to be explained by the elasticity 

 of the earth's crust ? 



The instruments are certainly sensitive to small loads 

 close to their bases of support. After spending about 

 twelve or fifteen hours within a distance of from three to 

 fifteen feet of the pendulums, it was found that the records 

 always showed a gradual recovery from the strain imposed 

 on the rock floor by one's weight. It may be that the 

 movements of the booms are to be attributed to the water 

 load operating in the same way. It is hoped that a quan- 

 titative examination of an extended series of records will 

 enable the nature of the deflections of the vertical to be 

 ascertained. 



In the meantime it is certainly a matter of interest that 

 such deflections are taking place, and that these appear to 

 be related to the water load. 



In conclusion, I would desire to express my great in- 

 debtedness to both Professor David and Father Pigot for 

 constant advice and assistance in connection with this 

 work ; to the latter especially for his advice and guidance 

 in completing the installations which he himself commenced 

 but was unable to complete owing to his visit to Europe ; 

 and for his most generous help in the preparation of this 

 paper. 



