THE SEINE, THE MEUSE, AND THE MOSELLE 
237 
found so great difficulty in deepening its valley and thus saving 
its branches from capture b}'' its neighbors? The chief cause of 
this difficulty must be looked for in the u})lift of the Ardennes, 
across whose resistant rocks the lower Meuse has, during Tertiaiy 
time (perhaps only during later Tertiary time), been cutting its 
grand gorge. Like the highlands #of the middle Rhine, the 
Ardennes consist of ancient and deformed rocks which have 
once been reduced to a peneplain of moderate relief drained 
idle streams,* but across which the Meuse is now actively cutting 
a deej) transverse valley in consequence of the strong uplift of 
the region. While the peneplain was yet a lowland the Meuse 
was comparatively safe from depredations, but during the eleva- 
tion of the peneplain and thereafter, great difficulty must have 
been experienced in deepening the valley. The Moselle must 
also have had some difficulty in deepening its valley through 
the uplifted highlands of the middle Rhine, but the uplift there 
does not seem to have been so great as it was in the Ardennes, 
and thus the Seine and the Moselle seem to have gained an ad- 
vantage over the unlucky river between their headwaters. It is, 
indeed, remarkable enough that the Meuse is still able to main- 
tain its course across the uplifted Ardennes, and its success can 
only be explained by regarding it as an excellent example of an 
antecedent river. It has battled manfully to preserve its course, 
and in this it has been wonderfully successful, for the highlands 
*Thi.s view of tiie history of the Ardennes is strongly presented in an essay by Pro- 
fessor de Lapparent, entitled “ L’age des formes topdgraphiques ” (Rev. des questions 
scientifiqnes, October, 1894) ; but there is one conclusion that he announces from which, 
if I understand him correctly, I must differ. Professor de Lapparent states that, at the 
beginning of Tertiary time, when the Ardennes were denuded close to the level of the 
sea, “the streams there circulated capriciously and almost with out slope on the sur- 
face of a region devoid of relief.” The “ capricious ” .irrangement of the streams seems 
to me very unlikely. Inasmuch as the present drainage of tlie Ardennes is for the 
most part accomplisheil by a rectangular system of streams, which follow longitudinal 
courses along the weaker strata and transverse courses across the stronger strata, it 
seems advisable to picture the peneplain to which the Ardennes were reduced as still 
possessing faint residuals of the many ridges that once rose above the peneplain, and 
to conceive the streams as e.xhibiting a well-adjusted relation to the structures, such 
as they would have slowly and laboriously acquired during the making of a peneplain 
from a once mountainous region of disorderly structure. The present rectangular 
streams wouhl then be, not the readjusted successors of :i capricious system of di-ainage 
on the peneplain, but the persistent successors of the laboriously adjusted streatns of 
pre-Teriiary beginning. If some of the streams of the Ardennes now exhibitcapri<'inus 
courses, unrelated to the structure in which their valleys are incised, they may be the 
successors of late Tertiary streams that had lost the adjustment of maturity in the 
meandering of old age, or they may be inherited fi-om courses that were assumed on a 
cover of unconformably superposed strata of late (Iretaceous or early Tertiary date, 
now all strippeil off; but, as far as I have seen the region and studied the maps, capi i- 
ciouH streams of this kind ilo not prevail. The characteristic rectangular streams aro 
well shown on slieets 48 and .‘it of tlie Helgian topogranliical maps; scale, 1 : 4u,nno. 
Ifi 
