32 BULLETIN OF THE LABORATORIES 



of an eroded col that one is apt to be misled. In the case of the true 

 col not only the gradient of the rock floor of the valley descends from 

 the location but also the general topographic surface descends in a di- 

 rection at right angles to the true divide, while in case of the pseudo- 

 col the general topographic surface forms a continuous plain across the 

 new system and the apparent divide as indicated by adjacent drainage 

 lines is the balance line between the two cycles and is evidently migrat- 

 ing rapidly from the new drainage axis. Field illustrations of this pe- 

 culiar topographic form will be given and discussed later. 



