Prof. R. Tate drew the attention of the Society to the exis- 

 tence of this interesting formation, and referred its origin tO' 

 ''the accumulation of exfoliated shell substance, washed out. 

 of the incoherent shell banks." This seems a plausible ex- 

 planation of its origin, and, as such, does not fit in to the 

 phenomena witli which we are dealing in this paper. The 

 natural whiting forms by a rearrangement of recent shelly 

 material, and not from solution of the older Tertiary lime- 

 stones as in the case of the travertine deposits. 



The chemical action which has led to the disappearance of 

 the Eocene limestones can be easily determined. Practically 

 all the rain that falls in the district is retained in the land 

 or in the subsoil, therefore the whole of the carbon dioxide 

 in solution (HoCOo) becomes locally available in setting up 

 the initial chemical change. During the wet months of the 

 year the porous limestones would become saturated with rain 

 water, and a certain portion of the caFcium and magnesium 

 carbonates would pass into solution when attacked by the free 

 carbonic acid in the water. The dry months of summer 

 cause a desiccation of the superficial stratum, and the mineral- 

 charged waters are, in consequence, drawn towards the surface, 

 and at a point where evaporation becomes possible the free 

 carbonic acid escapes, leaving a calcareo-magnesian carbonate, 

 or dolomitic limestone, as a crust. If such a process of change 

 is continuous (and it must be so as long as the climatic condi- 

 tions remain as at present), it is only a question of time when 

 the marine limestones will suffer a complete reconstruction 

 under new chemical combinations. The few scattered outliers 

 of this formation which occur in the district, and their vary- 

 ing thickness, mark the differential degi'ees in which this work 

 of chemical change is being effected at respective points. It 

 is a slow process, and the amount of material that has been 

 removed is very great, but is not greater than has been 

 achieved by the same acidic solvent in other parts of the 

 world. 



In addition to this secondary deposit of dolomitic traver- 

 tine we have to account for the considerable deposits of 

 sodium chloride and gypsum, which are also characteristic of 

 this country. Common salt, scraped from the beds of the 

 lagoons is exported annually from the district to the extent 

 of 35,000 tons- ; and in most of the lakes gypsum forms in 

 the saliferous layer which extends to a tew feet from the sur- 

 face. The more soluble sodium chloride assumes the solid' 

 and liquid conditions alternately with the dry and wet sea- 



*The export of salt during the ten years, 1890-1899, has risen from 5,598^ 

 tons to 35,05S tons. 



