658 MART us R. CAMPBELL 



from the question the law of migration of divides will cause 

 modifications in all the streams within the area affected by the 

 uplift or depression. This applies to streams belonging to the 

 same system, as well as those belonging to different systems, 

 and operates as follows : Wherever two streams are contesting 

 for a divide, and the surface is tilted in a direction perpendicular 

 to that divide, the streams located on the side of the great- 

 est tilting will rob their adversaries of the contested ground and 

 the divide will migrate indefinitely, depending upon the amount 

 and continuation of the movement and the size of the oppos- 

 ing streams. Under such conditions the smaller streams will 

 extend their head branches directly toward the line of greatest 

 uplift, and consequently will arrange themselves at right angles 

 to, and flow away from the axis of uplift, or toward the axis of 

 depression. The larger streams which cross the axis, will be 

 variously affected by the movement, depending upon the volume 

 of the stream and the rate of the uplift. If the volume of water 

 is great and the uplift sufficiently slow, the river may corrade its 

 channel as fast as it is elevated, and so maintain its position. If 

 the rate of uplift is more rapid than that of corrasion, the stream 

 will become ponded and probably robbed of a large portion of its 

 drainage basin by a more favorably located rival. 



The small branches, having assumed a course at right angles 

 to the axis, will carry their waters away from the axis until they 

 pass beyond the region affected by the tilt, or join some longi- 

 tudinal stream of sufficient size to have maintained its course 

 despite the uplift. 



The major streams tend to arrange themselves parallel with 

 the axial line, hence they will flow approximately at right angles 

 to the minor drainage lines, producing a rectangular system. 

 A large stream flowing originally parallel with the axis will tend 

 to retain this parallelism, unless it is tapped by some lower 

 stream, and in that event the chances are that it will be tapped 

 by a stream flowing perpendicular to the axis, and the major 

 stream will be transferred to a lower course. In no case, unless 

 local obstacles interfere, will the stream pursue a diagonal 



