59 



{d) The rim of the crater on the side where the subsidence 

 has taken place is broken in outline, and lower than the 

 rest. 



(e) The ash beds, which are distinctly stratified within the 

 limits of the vent, are seen to be faulted as the result 

 of the subsidence. 



This fracture of the base of the mountain on one side has 

 given a most instructive section of the beds for a thickness 

 of some 60 or 70 ft. Very large blocks of fossiliferous Eocene 

 limestone, as well as the grey and red dolomite, common in the 

 tufaceous material of Mount Gambler, are seen protruding 

 from the ash beds. One block of limestone measures fully 

 20 ft. in diameter. It might have been regarded as a natural 

 outcrop had not the evidence been clear that it rests upon the 

 ash, which has been disturbed by the force of its impact. 



Ejected blocks of lava, whilst common at Mount Gambier, 

 are rare in the cone of Mount Schank, and so far as I examined 

 the ejected material there is less indication of mud and sand, 

 the finer material of the cone being composed almost entirely 

 of ash, papilli, and scoriae. 



The Lava Field. 



One of the most interesting features of Mount Schank is the 

 lava field, which occupies the comparatively level ground on its 

 western side, and may be estimated as extending about one and 

 a quarter miles laterally to the Mount and tliree-quarters of 

 a mile wide. Tenison Woods, in his '"Observations" (p. 274, 

 et seq.), says : "It seems, for many reasons, very clear that 

 this stream proceeded from the ancient crater, and not from 

 the more modern one." The reasons given for this con- 

 clusion are purely of a theoretical character, and do not rest 

 on inductive observations. In a later passage he says : 

 "This line of lava was, then, a current from Mount Schanks 

 ancient crater; but, in supposing it to be so, it is not easy 

 to account for the broken undulatory character of the scoriae.' 

 This extraordinary arrangement of the lava, which was a puzzle 

 to Tenison Woods in applying his theory, supplies one of the 

 moEt important lines of proof which accounts for its existence. 

 Tlie inapplicability of Woods' theory to the facts is seen in 

 that the lava thins out as it approaches that side of the Mount 

 from whence he supposed it to have originated, and we have 

 already shown that what he considered an "older crater'' is 

 nothing more than a local subsidence of a similar kind as has 

 occuiTed around the Mount Gambier crater. 



A careful examination of the lava field reveals tlie interest- 

 ing fact that it has not been the product of one great outflow 

 of lava proceeding from a single vent, but rather a network of 



