8 



Australia the lower Tertiary limestones are associated with 

 considerable saline and gypseous ingredients, but the condi- 

 tions in "Y'orke Peninsula are piuch more favorable for the 

 conservation of these minerals, because there is practically no 

 outward drainage for the waters of the district. The distri- 

 bution of sulphur is very general in the organic, as well as 

 inorganic, world, and, therefore, offers no difficulty in account- 

 ing for the presence of gypsum under the conditions named. 

 Sulphate of magnesia is easily soluble, and would react on the 

 calcium carbonate that haa passed into solution by excess of 

 carbonic acid, forming the resultants, sulphate of lime and 

 bicarbonate of magnesia; the former crystallising out as 

 selenite, and the latter, uniting with calcium carbonate, form- 

 ing the dolomitic travertine. 

 Importance of the Glacial Clay in the Physical Features. 



One of the chief determining factors in the physical features 

 of Southern ^orke Peninsula is, undoubtedly, the glacial clay, 

 which, as described in a previous paper, seems to underlie 

 most of the district. At Point Turton, on ^he north coast, 

 and in the sea cliffs a little west of Troubridge Hill, on the 

 south coast, the Eocene limestone is seen to rest directly on 

 the glacial clay. This formation of compact clay supplies the 

 base — the impervious floor, on which for the most part the 

 newer formations of the district rest. Had no such im- 

 pervious barrier existed, the superficial drainage would no 

 doubt have found its way to greater depths, and carried the 

 soluble minerals beneath the surface. As it is, at present 

 the chemical reactions have largely taken place above this 

 floor line, and have become intensified by evaporation and 

 concentration carried on through ^ very prolonged period. 



The depth of the lagoon floors below the normal level varies 

 from a few feet up to probably forty feet. At the outer rim 

 of the depression the ground usually has a gentle slope towards 

 the lake, with steep or nearly vertical cliffs near the water's 

 edge. As some of these basin-shaped hollows have been 

 excavated in glacial sands and clay, ^t is certain that, in 

 some cases, other agents besides chemical solution have been 

 responsible for their excavation in part. It is noticeable 

 that the cliffs surrounding the lagoons are often lower or more 

 sloping on the north-east side than the opposite. As the 

 prevailing winds are from the south-west, it will be seen that 

 in such instances the lower banks are in the windward direction. 

 The beds of the lagoons are for the most part dry for a con- 

 siderable part of the year, and when in this condition they 

 expose a level surface of fine silt that might easily be carried 

 l)y the wind. If a crust of salt forms over the mud flats 



