230 
THE SEINE, THE MEUSE, AND THE MOSELLE 
higher up than the upper Moselle have been diverted. Looking 
at the Aire, it appears that the present radius of the meanders 
is much smaller than the radius of the swinging valley that is 
followed by the little Bar, and from this it may be inferretl that 
not only the existing Aire but the drainage of a still larger basin 
once ran down the valley of the Bar. Perhaps the upper Ornain 
represents something of the additional volume that the Aire 
once po.ssessed, but I cannot find direct indication tliat such is 
the fact. The maps on the scale of 1 : 80.000 seem hardly of 
suHicient detail to enable one to solve this j)hase of the problem 
by indoor study alone. The whole subject calls for extended 
study in the field, and a more interesting problem could hardly 
l)e selected for a summer’s work. 
Another subject to which no reference has yet been made is, 
nevertheless, of fundamental importance to the whole ])roblem : 
Why is it that the Seine and the Moselle are waxing at the ex- 
j)ense of the waning Meuse ? Why do they possess an advantage 
while tlie intermediate stream is at a disadvantage ? How could 
the Meuse ever have gainetl so large a drainage area as it once 
must have had, if at a later stage of its history it was to be so 
closely sliorn of its branches ? This is too large a problem to 
enter far ui)on now, but it contains two elements that may be 
Indefiy stated. One is that many ot the streams in the region 
of the Meuse are longitudinal streams — that is, they run chiefly 
along the strike of the weaker strata and their valleys have long 
ascending slopes on the eastern side and more abrui)t sloi)es on 
tlie western side. The highlands reached by these slopes are 
determined by the outcrop of more resistant strata than those of 
the valleys wliich the streams have excavated. Longitudinal 
streams of this kind I have called ‘'subsequent,^' l)elieving that 
they cannot have originated in immediate conseciuence of the 
original slopes of the land surface when it first arose above the 
sea, but that their opportunity came later when the wasting of 
the weak strata allowed the headward growth of streams along 
tlieir strike, after the manner ex})lained in connection with the 
adjustments of the Marne and its branches near Chalons. The 
Meuse and at least some of the branches that it once had there- 
fore seem themselves to have been the result of dejjredations 
committed on the territory of some still earlier river or rivers, 
and if this is true, the sympathy that the present impoverished 
condition of the Meuse excites is not deserved. 
However this may be, why is it that the Meuse has lately 
