iossiliterous limestone has become more or less altered by 

 solution and redeposition, which in some cases have entirely- 

 obliterated the organic features of the rock. Over the coun- 

 try from which the Eocene limestones have disappeared there 

 aiso occur important secondary deposits which have ap- 

 parently been formed by the destructive chemical agents operat- 

 ing on the older limestones; these secondary deposits are 

 mainly dolomitic travertine, calcium carbonate, sodium 

 chloride, and gypsum. 



Secondary Deposits Resulting from Chemical Solution. 



Dolomitic travertine, in varying thickness, is very generally 

 distributed over the district, and in many instances rests 

 directly on the glacial clay. It is improbable that the tra- 

 vertine limestones have been formed by the segregation of car- 

 bonate ot lime from the glacial beds wdiich underlie them, n2 

 the latter seem to be singularly destitute of calcareous matter. 

 The thickness of these beds, in some cases, amount to no less 

 than twenty feet, which demands a very considerable reposi- 

 tory of calcium carbonate in the subsoil to produce so thick 

 a travertine crust. It is not improbable that the Eocene 

 limestones have been entirely substituted over a great extent 

 of the country under review, passing by solution and recon- 

 struction into the dolomitic and other equivalents which have 

 formed in close proximity to the original limestone beds. 



Much of the calcium carbonate, when in a state of solution, 

 would doubtless be carried some distance from its source by 

 subterranean waters, so that an area that is by this means 

 losing its rock material will naturally exhibit irregularities of 

 surface, including saucer-shaped depressions. In most lime- 

 stone districts loss of material by solution leads to the forma- 

 tion, not only of subterranean caves, but superficial depres- 

 sions popularly known as "crab holes," ''swallow holes," or 

 "Bay of Biscay country." The existence, therefore, of 

 numerous sunken areas in Southern Yorke Peninsula can be 

 naturally correlated with the disappearance of the Tertiary 

 limestones from much of the lagoon country. 



In some parts of the Great Salt Marsh, and along the West 

 Coast, as well as behind Cape Spencer, there is a remarkable 

 deposit of almost pure carbonate of lime, perfectly white, and 

 with the physical features of whiting. It is undoubtedly a 

 ■secondary depost of calcareous material that has accumulated, 

 not from solution, but from mechanical waste. I was not 

 able to visit the localities where it occurs, but I am informed 

 I)y residents of the district that it exists in veiy pure deposits 

 up to seven feet in thickness, or even more. In 1889'^ 



*Tran?. Roy. Soc. S. Aus., vol. XIIL (1889-90), p. 113. ' 



