336 THE LAKE GEOKGK SENKUNGSFELD, 



the water's edge, 30 feet high, at an angle of 26'^. The same 

 tongues project out behind to the leeward side (indicated in 

 Plate vii.). Probably a like origin may be assigned to these 

 gravel-banks. They are due, I think, to the action of the storms 

 on the lake when the latter is full. The winds are confined by 

 the gigantic wall of the fault scarp, and rush along the latter, 

 driving forward the angular talus with which the scarp is littered. 

 Gradually the angular fragments are rounded and collect at 

 the ends of the Lake, in much the same way as on a coral reef 

 the clinker gradually accumulates towards the lee side of such 



reef. 



V. Economic Aspect of the Senkungsfeld. 



Little attention has hitherto been paid in Australia to the 

 relation between physiography and economics, which fact may 

 justify the following brief digression. In the first place mention 

 may be made of the gold alluvial rendered available for human 

 industry by the deviation of water from the old Lake George 

 River. In 1860 there was a gold rush to Diamond Hill, then 

 called the Brooke's Creek Gold Rush. From the numerous shafts 

 sunk, as well as from the recollections of old residents, this would 

 appear to have been fairly successful. Several years ago, a few 

 diamonds were washed out of this same gravel, and hence the 

 change of name. Grove Creek gravels do not seem to have been 

 payable. The miners experienced great difficulty in cutting 

 througli the layer of ferruginous cement at the bottom of the 

 gravels, and most of the claims were therefore abandoned. Now 

 the old wives of the district use the pipeclay for whitening their 

 hearths, without experiencing much curiosity as to how it got 

 there. 



The graph of Lake-variation is inserted {vide tig. 4) to show 

 the periods when Lake George really was a lake. Such were the 

 years 1816-1830, 1852, 1864, 1874-1900. Since 1900 the Lake has 

 been shrinking, and was practically dry in 1905. A local flood 

 has practically no effect on the Lake. The dry silt acts as a huge 

 sponge, and absorbs a covering of several inches of water, brought 

 down by Deep Creek or some other feeder, in the course of a 



