170 ^ J. T. Jutson: 



AH greenstone clifts bordering lakes have not pronounced caves- 

 and hollows at their base; but some hollowing out, although per- 

 haps only a small scale, can generally be detected. If the rocks are 

 comparatively soft or finely schistose, the rate of ordinary weather- 

 ing on the face of the clifi by insolation and the action of rain, may 

 keep pace with or, exceed the rate of weathering at the base, with 

 the result that no pronounced hollows or caves are formed; and the 

 angle of slope of the cliff will depend on the ratio between the two 

 forces. The prominent greenstone cliffs on the western shore of 

 Lake Goongarrie, close to the town of Comet Vale, afford excellent 

 illustrations of fairly steep slopes with practically no hollows at tlie 

 base. Here the respective rates of erosion at the Dase and on the 

 upper portion of the cliff appear to be about equal. 



The writer believes that " exsudation " also acts to some extei\t 

 away from the lakes in the hollowing out of granite boulders, and 

 in the formation of caves and hollows beneath the hard caps of 

 the lines of clifJs known as "breakaways." It is proposed, how- 

 ever, to discuss these questions in another paper. 



Rock jfioors are exposed — or coated with mere films of silt — in at 

 least portions of many lakes. The rocks may be ancient sediments 

 or igneous rocks, and are frequently " soft " and easily broken. 

 When the floor is free from surface water, the underground water 

 is drawn to the surface by capillary attraction, evaporation takes 

 place, and an efflorescence of salts (chiefly common salt) occurs on 

 or near the surface of the rocks. The surface of the latter tends to 

 break down into a meal, which is soon swept away by wind or 

 water. The writer has collected numeroiis specimens of these 

 rocks, which showed little salt deposited on the surface, but which 

 must have contained in solution a comparatively large amount, as 

 alter a few days common salt was thickly deposited as an efflores- 

 cence, and some specimens had crumbled to pieces. On these rock 

 floors, exposed as they are for the greater part of the year to the 

 sun's rays, the amount of direct and indirect disintegration by 

 salt efflorescence is probably considerable, and an appreciable 

 factor in the general erosion of the land. 



The Results of the Process. 



The results of the process of " exsudation " as here considered, 

 aided by other apparently subordinate processes, have already 

 been partly stated. They may. however, be now briefly sum- 

 marised. Thev include : 



