456 L. A. COTTON. 



Fault movements are represented on the records by 

 relatively rapid movements of the booms. In most cases 

 the movement occupies only a few hours, resulting in a 

 permanent displacement of the zero position of both booms, 

 these faults are generally unaccompanied by any earth- 

 quake shocks. They sometimes occur in the same sense 

 as the preceding slow movements of the pendulum booms 

 and at other times in the opposite direction. The position 

 of the fault plane and the direction of the downthrow with 

 regard to the position of the instrument no doubt deter- 

 mines this relation. It is hoped that the chief lines of 

 fracture may be located by observations from all three 

 instruments. 



It is, however, in the slow deflections of the vertical 

 that the main interest of the investigation lies. These 

 movements may be related chiefly to the water loads or 

 may be due to other causes, but it seems almost certain 

 that the former cause is in operation. More light will no 

 doubt be cast upon the problem by further investigation. 



Interpretation of the Becords. 

 It is as yet premature to offer definite conclusions, but 

 there are certain suggestions that may be considered. Is 

 it possible that the deflections of the vertical, which are 

 undoubtedly taking place at Burrinjuck, are due to isostatic 

 adjustment ? 



In this connection we have involved the question of local 

 versus regional isostacy. Barren's investigations of the 

 strength of the earth's crust are strongly opposed to the 

 possibility of such a relatively small mass as the water 

 content of the Burrinjuck Reservoir having any isostatic 

 effect. On the other hand Hayford and Bowie consider 

 that isostatic adjustment may affect areas as small as one 

 square mile in extent. 



Is it possible that both these views may be reconciled? 





