not unfavorable to such a supposition to a limited extent. 

 There are, for example, indisputable proofs that since the 

 close of the Tertiary period the land has risen several feet, 

 and this elevatory movement has led to the ;L'etreat of the 

 sea from a low-lying belt of country, running north and south, 

 uniting HardwicKe Bay and Sturt Bay. These evidences of 

 recent geological change were noted by Professor Tate in a 

 paper read before this Society in 1890. It must be observed, 

 however, that the physical features of this raised sea bed are 

 distinctly different from the lagoon country which occupies 

 somewhat higher ground. The erstwhile narrow strait which 

 has becomq dry land is known as the "Great Salt Marsh." Its 

 bed is comparatively level, and, whilst stretches of water 

 occur at intervals along its course, it lacks the features of the 

 circular lagoons on the higher ground, and does not deposit 

 salt to anything like the same extent as many of the lagoons. 



The physical features of the Great Salt Marsh are per- 

 fectly consistent with those of a raised sea bed, but the cir- 

 cular salt lagoons are not. No form of marine erosion can 

 produce saucer-shaped depressions below the normal level. 



Various Origins of Lake Basins. 



The origin of lake basins can usually be referred to one or 

 other of three agencies : — 



(a) Ice action, in which a rock basin may be formed by 

 the eroding power of land ice ; or, otherwise, morainic material 

 thrown across a line of drainage, may dam back the waters, 

 and thereby form a lake. 



(b) Wind acting on the surface of bared silt or clay may 

 scoop out hollows, the axis of erosion being in the direction 

 of the prevailing strong winds. 



(c) Chemical solvents acting upon rocks, in situ, and 

 by removal of material in solution, produce superficial depres- 

 sions of greater or lesser extent. 



[It is not necessary to refer here to such minor causes 

 of lakes as marginal lagoons, impounded by blown sand along 

 some coasts, or crater lakes of extinct volcanoes, as they are 

 local features, and their origin is generally sufficiently mani- 

 fest.] 



Of the three principal agents, mentioned above, which 

 may give rise to lakes, ice is out of the question in explaining 

 the lagoon phenomena of Yorke Peninsula, for, whilst the 

 district carries abundant evidences of an extinct ice field, the 

 glaciation was long anterior to the formation of the present 

 surface features, and there is nothing in the physical char- 

 acteristics of the lakes to suggest either rock basins or 



