THE WORK OF RUNNING WATER, 173 



diverted, as many of its tributaries have been. Even its course across 

 the Cascade ranges is believed to be antecedent. ^ 



Another peculiarity of valleys and streams resulting from changes 

 of level is illustrated in Fig. 2, PI. XIV (southern California). The 

 main A^alleys of this part of the coast were developed when the land 

 stood considerably higher than now. Later the subsidence of the 

 coast converted the lower ends of the valleys into bays or fiords. The 

 bays were then transformed into lagoons by deposition. Subsequent 

 rise of the land or depression of the sea allowed the drainage from the 

 old lagoons to cut across the deposits which had converted the bays 

 into lagoons. The result is an old, wide valley above, suggested by 

 a young one below. 



If the warpings were considerable, much more decisive changes in 

 drainage would result. Suppose the drainage of a given region to be 

 represented by the streams in Fig. 163. If there is uplift along the 

 axis 1-2, that part of ac above the axis of uplift would be ponded^ 

 or at least have its velocity checked, while the flow of some of the 

 tributaries of d would be accelerated, and might work back and cap- 

 ture the other stream (Fig. 164). — ^ 



Crustal warping was one of the conditions under which th|e Tennessee 

 achieved its present anomalous course, and its history^ is| illustrative 

 of the complex changes which drainage suffers when war|)ing affects 

 the area where the rock structures are of unequal resist arfce. At the 

 close of the Cretaceous cycle of erosion, when the Appalacjhian Moun- 

 tains had been reduced to a peneplain, the waters falling in the area 

 now drained by the upper course of the Tennessee flowed south-south- 

 west to the Gulf in a stream (the Appalachian River, a, Fig. 165) the 

 lower part of which had the general position of the Coosa and the Ala- 

 bama. 



To the west of the Appalachian River, shorter streams flowed west 

 and southwest into the Mississippi embayment (Fig. 165), by courses 

 which are not now definitely known. The succeeding cycfe of erosion 

 was inaugurated by uplift and deformation of the peneplain. The axis 



^ Russell. Rivers of North America, p. 279. 



2 Hayes, Physiography of the Chattanooga District, 19th Ann. Rep., U. S. Geol. 

 Surv., Pt. II, pp. 9-58. See, also, Hayes and Campbell, Geomorphology of the South» 

 em Appalachians, Nat'l Geog. Mag., Vol. VI, pp. 63-126.- 



