308 /. T. Jutson — Interpretation of the Dry Lakes 



in almost any direction. Many vary from approximately north and 

 south, through north-north-west, north-west, to west-north-west. 

 Some trend north-easterly, and others are approximately east and 

 west. Probably, however, in the main there is an approximation to 

 north and south with variations to the east and to the west of north 

 respectively. When the term " western shore " or "western side" 

 is used in this paper, it is meant to include not only the true 

 western shore when the lake trends approximately north and south, 

 but also the south-western or north-western shore when the lake 

 trends north-west or north-east respectively, because the remarks 

 below as to rock-floors and cliffs apply to the westerly shores as a 

 whole, despite the deflection of the trend of the lakes from north 

 and south. 



Along the western shores of many, and along the northern shores 

 of some, of the lakes, rock-cliffs and rock-floors occur. The eastern 

 and southern shores are usually destitute of these features, which 

 are replaced by silt floors, sand dunes, and sand plains. 



The cliffs are rocky, generally steep, and frequently form very 

 prominent features in the landscape, when they project as a series of 

 bold headlands into the lake. So far as known, the commonest 

 rocks forming the cliffs are what may be called "greenstones", 

 a field term which includes many kinds of basic igneous i'ocks, 

 which, however, need not he enumerated here. Cliffs are also 

 formed of "jaspers" (quartz haematite schists) and granites. At the 

 base of the cliffs rock floors of similar or associated rocks frequently 

 occur. These floors are of such smoothness that the writer has 

 termed them "billiard-table rock-floors". They may be visible 

 outward from the base of the cliffs only for a chain or two or they 

 may extend for hundreds of yards up to a mile or more. Such 

 floors tend to be covered by the fine silts of the lake, and as these 

 silts vary in thickness and superficial area (although little is yet 

 known as regards their thickness), the extent of the floors exposed 

 also varies. 



The rocky cliffs are being worn away by various agents of erosion, 

 the nature of which is described when discussing the meaning of the 

 rock-cliffs and floors. 



Some lakes may have no rock-cliffs on any side, but the writer is 

 not aware of any with cliffs on the eastern side. It is possible that 

 such last-mentioned cliffs nevertheless do occur, but if so they must 

 be rare. 



Small valleys may enter lakes, and the lower portions of such 

 valleys may, by lateral erosion, become arms of the lakes. 



Examples of Lakes with the Featdres besceieed in South- 

 Central "Western Australia. (Map I.) 



Kurrawang Lakes, south of the railway line between Kalgoorlie 

 and Coolgardie. According to C. S. Honman's maps and descriptions ^ 

 the lakes are bounded on the west and north by rock-cliffs, and on 



1 Bull. 56, Geol. Surv. W. Austral., 1914, pis. i, ii, fig. 1, pp. 10-12, 34. 



