National Geographic : 1896 Jul
THE SEINE, THE MEUSE, AND THE MOSELLE found so great difficulty in deepening its valley and thus saving its branches from capture by its neighbors ? The chief cause of this difficulty must be looked for in the uplift of the Ardennes, across whose resistant rocks the lower Meuse has, during Tertiary 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 by idle stream s,* but across which the Meuse is now actively cutting a deep 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 * This view of the history of the Ardennes is strongly presented in an essay by Pro fessor de Lapparent, entitled " L'age des formes topographiques " (Rev. des questions scientifiques, 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 " arrangementof the streams seems to me very unlikely. Inasmuch as the present drainage of the Ardennes is for the most part accomplished 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 exhibiting 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'would then be, not the readjusted successors of a capricious system of drainage on the peneplain, but the persistent successors of the laboriously adjusted streams of pre-Tertiary beginning. If some of the streams of the Ardennes now exhibit capricious 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 from courses that were assumed on a cover of unconformably superposed strata of late Cretaceous or early Tertiary date, now all stripped off; but, as far as I have seen the region and studied the maps, capri cious streams of this kind do not prevail. The characteristic rectangular streams are well shown on sheets 48 and 54 of the Belgian topographical maps; scale, 1: 40,000.