664 MARIUS R. CAMPBELL 



the streams, for that is a matter of slow development. If the 

 uplift rises athwart the stream, the first recognizable feature is 

 the change of grade in the river profile and the formation of a 

 barrier at the point where the axis crosses the stream. If the 

 stream is flowing over soft, homogeneous rocks, corrasion may 

 take place so rapidly that no appreciable barrier is produced, 

 but as a rule we may expect to find some feature characteristic 

 of a revived stream at this point and pondingin the stream above 

 the barrier. 



{b) Remote movements showfi by the arrangement of the mifior 

 drainage. — Movements which occurred in the remote past have 

 left no record where they crossed large streams, unless the 

 movement was so severe as to cause reversal but the minor 

 drainage lines may be marked by all of the characteristics 

 described in this paper. The divides may have migrated until 

 all of the stream basins are unsymmetrical, having the main 

 stream near one side and the minor drainage lines reaching out 

 toward the axis of uplift. Unless counteracted by geologic 

 structure, the rectangular arrangement of the drainage lines will 

 be permanent, so long as the crustal movement continues, or 

 until counteracted and obliterated by reverse movements. In 

 such cases if the change has not progressed too far it is gener- 

 ally possible to find cases of stream capture and other marks of 

 radical rearrangement. 



(<:) Very remote niovements showji by the arrangement of the 

 trunk streams. — As we go farther and farther back into the past, 

 the evidence becomes less and less perfect, until at last it is 

 only in the^arrangement of the great streams that we can find a 

 trace of the conditions then prevailing. This of course is unsat- 

 isfactory, since it is bare of all details, but in a broad way it out- 

 lines the movements which shape the main drainage-ways of that 

 distant age. 



(4) PERIODICITY OF STREAM CHANGES. 



There is another point which it is well to consider in the 

 application of the law of the migration of divides, and that is, 



