212 National Geographic Magazine. 



in the next three diagrams, figs. 16, 17, 18. Two adjacent syn- 

 clinal streams, EA and HB, join a transverse master stream, C, 

 but the synclines are of different forms ; the surface axis of one, 

 EA, stands at some altitude above baselevel until it nearly reaches 

 the place of the transverse stream ; while the axis of the other, 

 HB, descends near baselevel at a considerable distance from the 

 transverse stream. As lateral valleys, E and D, are opened on 

 the anticline between the synclines by a process similar to that 

 already described, the divide separating them will shift towards 

 the stream of fainter slope, that is, towards the syncline, EA, 

 whose axis holds its hard beds above baselevel ; and in time the 

 upper part of the main stream will be withdrawn from this syn- 

 cline to follow an easier course by crossing to the other, as in fig. 

 17. If the elevation of the synclinal axis, AES, take the shape of 

 a long flat arch, descending at the further end into a synclinal 

 lake basin, S, whose outlet is along the arching axis, SA, then 

 the mature arrangement of stream courses will lead the lake 

 outlet away from the axis by some gap in the nearer ascending 

 part of the arch where the controlling hard bed falls near to 

 baselevel, as at F, fig. 18,* and will take it by some subsequent 

 course, FD, across the lowland that is opened on the soft beds 

 between the synclines, and carry it into the lower syncline, HB, 

 at D where the hard beds descend below baselevel. 



The variety of adjustments following the general principle 

 here indicated is infinite. Changes of greater or less value are 

 thus introduced in the initial drainage areas, until, after attaining 

 an attitude of equilibrium, further change is arrested, or if occur- 

 ring, is relatively insignificant. It should be noticed that the 

 new stream courses thus chosen are not named by any of the 

 terms now current to express the relation of stream and land his- 

 tory ; they ai-e neither consequent, antecedent nor superimposed. 

 The stream is truly still an original stream, although no longer 

 • young ; but its channel is not in all parts strictly consequent on 

 the initial constructional form of the land that it drains. Streams 

 thus re-arranged may therefore be named original streams of 

 mature adjustment. 



It should be clearly recognized that the process of adjustment 

 is a very slow one, unless measured in the extremely long units 



* This figure would be improved if a greater amount of wasting 

 around the margin of the hard bed were indicated in comparison with 

 the preceding figure. 



