president's address. 17 



tion of potassium, converting the whole to a hydrated potassic 

 ferric silicate, and the characteristic greenish hue is assumed.* 



{3)The Continental Base. 



In illustration of the slope below the shelf, here termed the 

 continental base, a profile is selected extending seventy! miles 

 east-south-east of UlladuUa, and produced backwards to include 

 the coast range. Your attention is first drawn to the insigni- 

 ficant proportions of a lofty hill upon tlie left, 2,-500 ft. high, 

 compared with the depths of the ocean abyss of more than three 

 vertical miles. As a more forcible illustration, the point is 

 mai'ked to where Mt. Cook, IS[.Z.(r2,359 ft.) would reach if it 

 could be torn from its roots and sunk in the Tasman Sea. Then 

 note the abrupt angle of the continental shelf already discussed. 

 Between sixteen and eighteen hundred fathoms, another irregu- 

 larity occurs in the curve, which is also repeated in the model of 

 the section off Sydney (Plates i. and ii.). This latter inflexion 

 possibly continues the curves shown in Professor David's 

 section across the Blue Mountains and Sydney coal field. | So 

 that the Ulladulla irregularity probably represents a subfold 

 rather than a fault or a drowned continental shelf. 



Without excluding faulting as a minor agent, it is suggested 

 that the whole sweep of the diagram portrays an earth-fold of the 

 first magnitude; that it represents the further luall of a pressure- 

 trough driven hy a thrust from the east, a gigantic buckle which 

 is bending down the whole eastern coast of Australia. If so it 

 must be a component of a vast system. The uniform and recent 

 subsidence which extends from Torres Strait to Tasmania is in 

 harmony with this suggestion. For all Eastern Australia anil 

 Tasmania is to be regarded as a geographical unit. Absence 

 of earthquakes may indicate a temporary equilibrium, but if this 



* CoUett & Lee, Proc. Roy. Soc. Edinburgh, xxvi,, 1906, pp.238-278. 



t Not fifty-five, as inadvertently stated on the diagram. Mt. Sidney of 

 the Admiralty charts is Talaterang of the Lands Department maps. Milton 

 Hill is the north end of Kingiman Range. 



X David, Journ. Roy. Soc. N. S. Wales, xxx., 1896, PI. ii. 

 o 



