[Proc. Eoy. Soc. Victoria, 19 (N.S.), Pt. IL, 1906.] 



Art. IX. — Surface Tension as an Aid in Canyon Form- 

 ation, the production of Bad Lands, and in 

 River Capture. 



By J. A. LEACH, M.Sc. 



(With Plate XVII). 

 [Kead 13th December, 1906]. 



Being attracted by a statement made by Professor Miall that 

 the surface film of water was a veritable death-trap to many 

 small animals, my thoughts turned much to phenomena con- 

 nected with that remarkable film. 



This statement was soon seen to be true, mosquitos, water- 

 fleas (Daphnia), and many small pond animals have been seen 

 held close prisoners by this wonderful "top of the water." Other 

 animals, such as mosquito larvae and pupae, pond snails, hydra, 

 etc., were seen, however, to take advantage of it. 



It is well known that soap bubbles are due to this phenomenon, 

 while the sphericity of rain-drops is also caused by its action. 

 The necessity of droppers for medicine, of lips and spouts for jugs, 

 teapots, and other vessels is also due to the tendency of this sur- 

 face film to adhere to any body it might happen to wet. This 

 tendency to adhere instead of falling vertically downward is, I 

 hope to show, a most important factor in the denudation of the 

 earth's surface, especially in canyon production, by causing rapid 

 undercutting where there are softer beds. 



A hard surface layer covering softer rock will present conditions 

 favourable to the formation of a waterfall. Tlie water rushes over 

 the hard ledge, and falls to the eartli beneath. The swirl and the 

 splash .soon wear out a circular hole — a pot hole. If the ledge is of 

 some height, the water leaps over. The spray is splashed around 

 and the softer material under the ledge is worn out. Sooner or 

 later, the surface ledge breaks off and falls in. Thus the canyon 

 or gorge travels up stream. 



