THE SEINE, THE HEUSE, AND THE MOSELLE 
231 
miles from the elbow. The comparative narrowness of the trench 
both above and below the elbow of capture b}'- Toul would not 
lead us to expect an obsequent stream of much length, and I 
therefore suggest the following explanation of the rather surpris- 
ing length of the Ingressin. A little southwest of Foug is the 
narrowest part of the old valley, its narrowness here being due 
to the greater resistance of the middle Oolite, which form the 
highland through which it is cut. From these steep slopes it 
appears that a significant amount of waste has crept down into 
the valley trough, obstructing it more or less and producing a 
swamp of small dimensions. The beheaded Pagny seems to 
have been unable to hold its course through this obstruction. 
It probably accumulated for a time in a shallow lake above the 
obstruction, until on overflowing into the gorge at the elbow this 
j)art of its course reversed its direction of flow, and thus gave 
rise to an obsequent stream of a somewhat aberrant type which 
is now called the Ingressin. 
All this, however, only by way of suggestion. Further study 
of the geographical aspects of the country is necessary before 
this sugge.stion deserves acceptance. There need, however, be 
no doubt on the general problem concerning the diversion of the 
Toul from the Meuse to the Moselle, and to my mind the case 
would be perfectly satisfactory if no pebbles from the Vosges 
had ever been found in the valley of the Meuse below Pagny. 
The dimensions of the meandering valle\% the systematic form 
of its bluffs and curves, the gorge above and below the elbow of 
capture at Toul, the relation of the old valley plain in which 
the gorge was cut to the floor of the meandering valley that 
leads through the upland, and the accident that hapj)ened to the 
little side stream at Foug, all combine into so S3^stematic an 
arrangement of parts as to leave no doubt that an explanation 
which can account for them by a single and simifle process is 
their true explanation. 
The (liniinished Meuse . — Looking now again at the Meuse l)y 
CommercN' we must recognize it as a river whose volume has been 
diminished by the diversion of an important tributary to another 
river .sj'stem. Its volume having diminished, it is unable now 
to accommodate itself to the large curves of its vallcv and must 
instead advance in an uncertain course as it staggers along on the 
valley floor. Not 011I3' so; hiiving lost volume, it seems unable 
to maintain so gentle a slope as it had assumed when its volume 
was larger, for its tlood-|)lain now has every appearance of hav- 
