,102 THE BURDEEIN VALLEY- 



into gorges, but the angle ot declivity necessary for the 

 streams to form these gbrges would cause them to be short- 

 While all denuding processes lead eventually to the 

 formation -of a plaiyi or, in other words, the reduction of 

 the surface to base levels, and while an approximation 

 to this result is an indication of great age in the cycle of 

 erosion, the writer has come to the conclusion that the 

 nature of some rocks. leads to their producing surfaces of 

 low relief having a deceptive appearance of old age. 



If this view be correct, the greatest caution is necessary 



.in making physiographical deductions from the mere exist- 



ance of what appears to be a peneplain, since, without a 



close acquaintance with its geological structure, one could 



^not be certain that it is due to advanced old age in the 



.cycle of erosion. 



.'li;. 



