THE CONFORMATION OF THE ALPS

Denmark Hill, 10th November, 1864.

1. My attention has but now been directed to the letters in your October numbers on the subject of the forms of the Alps. I have, perhaps, some claim to be heard on this question, having spent, out of a somewhat busy life, eleven summers and two winters (the winter work being especially useful, owing to the definition of inaccessible ledges of strata by new-fallen snow) in researches among the Alps, directed solely to the questions of their external form and its mechanical causes; while I left to other geologists the more disputable and difficult problems of relative ages of beds.

I say “more disputable,” because, however complex the phases of mechanical action, its general nature admits, among the Alps, of no question. The forms of the Alps are quite visibly owing to the action (how gradual or prolonged cannot yet be determined) of elevatory, contractile, and expansive forces, followed by that of currents of water at various temperatures, and of prolonged disintegration — ice having had small share in modifying even the higher ridges, and none in causing or forming the valleys.

2. The reason of the extreme difficulty in tracing the combination of these several operative causes in any given instance, is that the effective and destructive drainage by no means follows the leading fissures, but tells fearfully on the softer rocks, sweeping away inconceivable volumes of these, while fissures or faults in the harder rocks of quite primal structural importance may be little deepened or widened, often even unindicated, by subsequent aqueous action.