Deposition of Bedded Tuffs. 23 



various a^es and localities is the nuly evidence in favour of the 

 former existence of these seas or lakes, and that, too, at times 

 in peculiar positions in reference to the modern surface drainage. 



Then, again, the tuffs, though stratified and very evenly bed- 

 ded, are not of uniform grain. Taking a small piece, stratifica- 

 tion is not evident. Dust and small scoriaceous fragments seem 

 mingled in confusion. It is the fine matter which brings about 

 the fissility, and yet the amount of coumiingled larger material 

 is considerable. There are, of course, well marked, beds of dust, 

 aflid equally well marked ones of coarse grain, but to my mind 

 the sorting is not as thom-ogh as it would have been had water — 

 that is, standing water —been the c-ause of the beddiniJ'. 



Mud torrents have been suggested, but they also are, I think. 

 out of the question. Such torrents wcmld, if they formed strati- 

 fied deposits at tiill, show false bedding, and not layer after 

 layer through a thickness of many feet, and a lateral measure- 

 ment of scores of yards. 



However, apart from this, we have at Mount Gambier evidence 

 which, I think, shows clearly that tuffs, as well stratified as 

 any of those of the Camperdown district, may occur under con- 

 ditions which forbid aqueous action. 



A brief .sketch of the geology of the district is necessary to 

 enable this evidence to be properly weighed. 



Tlie bed-rock over hundreds of square miles is a white lime- 

 stone mainly composed of polyzoal remains. This is of Bar- 

 wonian age ( ? Eocene;, aind is, as far as can be seen, quite 

 horizontal. It is extremely porous, and water-courses are absent. 

 There are, of course, many swallow holes, caves and underground 

 drainage channels, so that many of the irregularities of the sur- 

 face are undoubtedly due to subterranean solution. This point 

 may be considered unfavourable to my view, so that I wish to be 

 properly considered. The general surface of the country is 

 slightly undulating, and the hills to the north of the town are, 

 for the most part, sandy. They are, in fact, sand dunes of 

 pleistocene or recent age, and vary someAvhat in the amount of 

 lime they contain, and consequently in the amount of con- 

 solidation they have undergone. In places they are loose yellow 

 sands, and in other places consist of the ordinary cross-bedded 

 dune-rock. A lew miles to the south of the town similar dime- 



