VOL. XVI. (3) THE LOWER SEVERN 249 
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This latter forms an “obsequent” stream. Below the 
divide the remainder of the streams ABCD continue 
A A F 
Fic. 5.—Diagram representing four streams, A BC D, flowing across the area now 
occupied by the Severn Valley, intended to illustrate the impossibility of 
“successive capture” and diversion of these streams as far as a divide 
formed above the portions represented by FG HI. Even if E could, by 
“working backwards,” divert D into its own channel, lit would itself, as a 
separate stream, cease to be. 
their course onward, as seen at FGHI. The effect, how- 
ever, of the first capture must have been that when the 
capturing stream lost its separate existence it merged in 
the united streams ED. How, then, could it go on to 
capture C, B and A “one after another” ? 
I admit that the headwater of a stream may advance 
into an area previously part of a different river system ; 
but not by any process of “cutting back” by the stream. 
For instance—let A, fig. 6, represent a divide between 
two streams B, C, flowing to D and E. If the upper part 
of the hill be formed by some material easily denuded, 
is 
maaiee 
Fic. 6.—Diagram of a divide, A, on a hill between the head waters of two streams B, C, 
flowing to D and E. When the relatively-soft formation of the upper part 
of the hill has been removed down to the harder rock beneath, the divide 
will shift westward to F. 
