306 J. T. Jutson — Interpretation of the Dry Lakes 



10 inches per annum, numerous "dry" lakes or playas occur.' 

 These have been described and the question of their origin has been 

 discussed by various authors. '■' They have been differently regarded 

 as due to glacial, marine, and wind action ; also as the remains of 

 old Tertiary rivers now largely obliterated by drifting sands; and 

 also (in part) as deformation basins. Most writers agree that they 

 liave been formed under subaerial conditions, and probably most 

 will ultimately agree that deformation is responsible for some at 

 least of the lakes, or has aided in their formation. 



The theory of a migration of the lakes has also been advanced by 

 the present writer. 



Like most other land forms the lake will probably, by further 

 research, be shown to be due to no single cause, but to a combination 

 of agents of different relative importance. 



Summary. 



This paper describes certain features of the " dry" lakes in South- 

 Central Western Australia. These features, which repeatedly occur 

 over a wide area, indicate, in the writer's opinion, that the lakes are 

 migrating westward; and that wind erosion is playing the dominant 

 part in such migration, and consequently in the present forms and 

 position of the lakes. Such features are the presence of rock-cliffs 

 and rock-floors on the western, north-western, south-western, and, 

 to a less extent, on the northern sides of the lakes; and the absence 

 of such cliffs and floors on the eastern, south-eastern, north-eastern, 

 and southern sides of the lakes, the place of such cliffs and floors 

 being taken by sand dunes, sand plains, and silts. The facts set forth 

 are regarded as confirming, to some extent, the idea of the late 

 H. P. Woodward that the " dry " lakes are due to wind action.^ 



^ Salts are precipitated on the lake floors on the evaporation of the transient 

 thin sheets of water, but so far as the writer is aware there is no thickness of 

 salt on any of the lakes. The terms " salt lakes " and " salt lake division " 

 are therefore misnomers. " Dry lakes " or " playas " more suitably indicate 

 the character of the lakes, but as the latter are frequently connected with one 

 another by defined or ill-defined channels, and as many undoubtedly lie along 

 the main drainage lines of the country, the writer has suggested the term 

 "stream-lake system" for this dual capacity of portions of the drainage 

 system. The terms "salt lakes" and "dry lakes" have become so firmly 

 rooted in local usage that they will probably remain. It is difficult to suggest 

 a suitable name for the physiographic division instead of " salt lake division ". 

 "Dry lake or central division" would perhaps be the least objectionable 

 of any. 



^ As to various theories, see J. W. Gregory, "The Lake System of 

 Westralia," Geog. Journ., June, 1914, pp. 656-64, map. See also C. G. 

 Gibson, Bull. 37, Geol. Surv. W. Austral., 1909, p. 12, and Bull. 42, Geol. 

 Surv. W. Austral., 1912, pp. 11, 12; J. T. Jutson, op. cit. , pp. 138-58, 

 and also Geog. Journ., December, 1917, pp. 418-37, map, figures; A. 

 Montgomery, Journ. Boy. Soc. AV. Austral., vol. ii, pp. 59-96, map, 1915-16; 

 J. W. Gregory, Geog. Journ., October, 1916, pp. 326-31; and C. S. Honman, 

 Bull. 71, Geol. Surv. W. Austral., 1917, p. 144, and Bull. 73, Geol. Surv. 

 W. Austral., 1917, p. 17. 



3 Geol. Mag., August, 1897, pp. 363-6. 



