Glacial Erosion in North Wales

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Abstract
I. The Form of Snowdon. An excursion around Snowdon, the highest of the Welsh mountains, in September, 1907, led me to the conclusion that a large-featured, round-shouldered, full-bodied mountain of pre-Glaeial time had been converted by erosion during the Glacial Period—and chiefly by glacial erosion—into the sharp-featured, hollow-chested, narrow spurred mountain of to-day. Or, to phrase it in somewhat more technical style, that a body of ancient slates, felsites, and volcanic ashes, greatly deformed in Palæozoic time and greatly worn down in successive cycles of Palæozoic, Mesozoic and Tertiary erosion, was reduced before the Glacial Period began to subdued mountain-form with dome-like central summit, large rounded spurs, and smooth waste-covered slopes, and with mature valleys drained by steady flowing streams which branched delicately headwards, with steepening slope, and which joined each other mouthwards in the accordant fashion that so systematically characterizes the drainage of all normally subdued mountain-masses. Also that this full-bodied mass was transformed during the Glacial Period, chiefly by the glacial excavation of valley-head cwms and by the glacial widening and deepening of the valleys themselves, irate a sharp central peak, which gives forth acutely serrated ridges between wide amlphi theatres: the serrated ridges changing into broad-spreading spurs as they are followed outwards ; the wide amphitheatres, backed by high rocky cliffs, opening by great rock-steps to irregularly deepened trough-like valleys, with oversteepened, undissected sides, sometimes smooth, sometimes of a peculiarly roughened slope; the smaller lateral valleys hanging in strikingly discordant fashion over the floors of the larger

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