200 
THE SEINE, THE MEUSE, AND THE MOSELLE 
of the lower Soucle, leaving the lower waters (the Petit Morin) 
as another diminished, beheaded stream ; hut inasmuch as this 
second capture must occur at a much later date than the first, it 
is natural to expect that the beheaded Petit Morin will, at the 
time of capture, have cut a much deeper valley through the up- 
land than was cut by the earlier beheaded stream, the Surmelin. 
The elbow of capture . — Let us call the sharp turn that the di- 
verted headwaters make where they join the diverting stream 
*■ the elbow of capture.” After the capture the rearranged water- 
course will cut a sharply intrenched valley above and below this 
elbow, for the diverted stream, of considerable volume, being 
turned into the head of the diverting stream, where the volume 
is zero, must immediately deepen its channel. As time passes 
the trench will disappear by widening, and hence the occurrence 
of such a trench may be taken as indication of recent rearrange- 
ment. Similarly the diminished, beheaded stream may be more 
or less obstructed by the detritus that is washed into its valle}’’ 
by small lateral branches; thus its flow may be delayed by 
swani])s or it ma}" be even held back in shallow lakes, as the 
Inn is held back in the lakes of Engadine, as described by Heim ; 
but this is also a relatively short-lived condition, for as time 
passes the beheaded stream will adjust its grade to the work 
that its diminished volume has to do and its lakes and swamps 
will disappear. 
In nearly all cases further shortening is enforced upon the 
beheaded stream below the elbow of capture. It deepens its 
valley slowly, while the reinforced subsequent diverter deepens 
its valley with relative rapidity ; hence the divide will be pushed 
away from the elbow of capture and the beheaded stream will 
be progressively diminished. The distance of the source of the 
beheaded stream from the elbow of capture may therefore be 
generally taken as a measure of the remoteness of the time when 
the capture took place. It not infrequently happens that a small 
stream is developed, flowing into the elbow of capture from the 
neighborhood of the source of the beheaded stream, and pro- 
gressivel}" lengthening as the divide is })ushed away and the be- 
headed stream is shortened. Let us call streams of this class, 
flowing against the dip of the strata, obsequent. They will mani- 
festly ])e wanting at elbows of recent capture, but they may attain 
a length of several miles if the capture occurred long enough ago. 
Now, look at the actual arrangement of the streams on the low- 
land west of Chidons and on the upland be}’ond the escarpment. 
