Surface Tension and Denudation. 55 



This is the explanation usually given, and probably it is correct 

 in most cases. However, at Coburg one day, when examining 

 the head of some " bad lands " with canyons nearly 20 feet deep, 

 this explanation was seen to be unsatisfactory for three reasons. 



1. The quantity of water that was doing the wearing out was 

 very small. It was only the small amount that flowed from a 

 few square yards of a uniformly sloping hillside, for there was no 

 stream, not even a gutter or runnel. It was too small a quantity 

 to splash about. 



2. This small amount of water could not have splashed high 

 enough to wash the softer subsoil from just below the surface 

 crust (a hard band several inches thick), which was at the height 

 of eleven feet (Fig. 2). 



3. There was no evidence of any fall of water at all. If a fall 

 took ]ilace from that height, there would be a pot hole at the foot 

 of the fall, or stones showing some signs of water splashing or 

 falling. But there was no trace of this. 



The usual explanation clearly did not account for the wearing 

 out, and the evident recent advance up hill of this gorge. As 

 no water was then running over, no other explanation presented 

 itself at the time. 



Shortly afterwards when at Heidelberg, the usual hollow was 

 noticed under the surface crust ; but it did not reach down to 

 the bottom. The crust was six inches thick. Then a 

 semicircular hollow about ten inches in diameter led to 

 a gently sloping piece of about fifteen inches down to the bottom 

 (Fig. 4.) Here, as no sign of any falling water could be seen on 

 the sloping base, there was obviously no splash at all. Thus the 

 water did not fall over. Close examination showed that the 

 water trickled down the surface crust and then adhered under- 

 neath it, the water surface forming the outer wall of a kind of a 

 pipe. The water then ran down, following under the surface 

 crust, over the soft material underneath, and so trickled this 

 down as liquid mud. Thus the earth was hollowed out right 

 under the crust, but it had not yet been worn away down to 

 the level of the bottom. Many little grooves could be plainly 

 seen where the water had trickled down, and carried off the 

 material. ^^ 



