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L. A. COTTON. 



the normal stability of the earth's crust at Burrinjuck. 

 There are two methods of attacking this problem. 



The first is by obtaining a set of standard readings with 

 the pendulums before any water load is imposed on the area. 



The second method is to apply geological tests as to the 

 stability of the earth's crust. 



It has unfortunately not been possible to rigidly carry 

 out the preliminary investigation by the first method. 

 Owing, however, to a period of drought, and to the neces- 

 sarily slow growth of the dam, the water load had not 

 exceeded about one-sixteenth of the total load before the 

 instruments were established. Moreover this load was 

 maintained fairly constantly for about nine months since 

 the first records were obtained. It is hoped that when the 

 results are worked out, that this period will provide a 

 sufficient test of the normal stability of the earth's crust 

 in this area. 



The second method will be investigated fully in a later 

 paper but may be briefly outlined here. 



A consideration of the topography and structural geology 

 of the district is necessary for the solution of the problem. 

 The Burrinjuck area is situated on a block faulted tableland, 

 which is deeply entrenched by the Murrumbidgee at 

 Burrinjuck. The rocks at Burrinjuck are of Devonian age, 

 are strongly folded, and consist of slates and limestones 

 into which are intruded granite, porphyrite and basalt. An 

 account of the broad geological features of the reservoir area 

 has been given by Harper. l The faulting is comparatively 

 recent, and slight earthquakes have from time to time been 

 felt in the south-eastern part of New South Wales. The 

 most marked of these of recent years occurred in the Cooma 



1 L. F. Harper. The Geology of the Murrumbidgee District near Yass. 

 Eecords Geological Survey New South Wales, Vol. ix, part 1. 



