124 T. C. CHAM BERLIN AND R. T. CHAMBERLIN 



gradually turned from its nearly vertical descent into a more nearly 

 horizontal course. 



The meaning of the short curve as distinguished from a longer 

 curve lies in the balance of the co-operating agencies. A good mantle 

 of vegetation when present measurably restrains the plunging waters 

 and somewhat softens the curve of transition. In the absence of 

 vegetation, the abrupt mesa-cliff on the one hand and the vertical 

 or even overhanging falls on the other are liable to develop. The 

 abrupt curve at the foot-slope in the tropical cases described is thus 

 referred to a co-operation of agencies in which (i) the absence of 

 talus-making causes, (2) the prevalence of minute surface decay, 

 (3) the restraint of vegetation, and (4) the concentration of the wash 

 toward the foot-slope are conjoined. This phase of action seems 

 to be prevalent in low latitudes, but not equally so in high latitudes. 



