By these semicircular concentric walls we can trace the retreat of the ice as it withdrew from the plain of Switzerland to the fastnesses of the Alps. It paused at Berne, and laid the foundation of the present city, which is built on an ancient moraine; it made a stand again at the Lake of Thun, and barred its northern outlet by a wall which holds its waters back to this day. Other moraines, though less distinct, are visible nearer the base of the Bernese Alps, and, above Meyringen, the valley is spanned by one of very large dimensions. Again, on the other side of the first chain of high peaks, the glacier of the Rhone, descending the valley toward the Lake of Geneva, has everywhere left traces of its ancient extension. We find the valley crossed at various distances by concentric moraines, until we reach the lake. There are no less than thirteen concentric moraines immediately below the present termination of the glacier of the Rhone, the one nearest to the ice, and the last formed, marking its present boundary. Others are visible half a mile, a mile, and two or three miles beyond, near the villages of Obergestelen and Muenster. One of the largest and finest of these ancient moraines of the glacier of the Rhone stands at Viesch, and extends across the whole valley, while the Rhone, already swollen by many mountain-torrents, has cut its way through it. Lower down, we meet with traces of other ancient glaciers, reaching laterally the main glacier, which occupied the centre of the valley: such was the glacier of Viesch, when it extended as far down as the village;[49] such was the glacier of Aletsch, when it added its burden of ice to that coming from the upper valley; such was the glacier of the Simplon, whose moraines, of less antiquity, may now be seen by the road-side leading over the Alps to Italy; such were the two gigantic twin glaciers that drained the northern slopes of the mountain-colosses around Monte Rosa and Matterhorn, united at Stalden, and thence, losing their independence, became simply lateral tributaries of the great glacier of the Rhone; such were, farther on, the glaciers coming down from all the side-valleys opening into the Rhone basin; such were the glaciers of the St. Bernard, and even those of Chamouni, which in those early days crossed the Tete Noire to unite below Martigny with those that filled the valley of the Rhone. Thus the outlines of this glacier may be followed from its present remnant at the summit of the Valais, where the Rhone now springs forth from the ice, to the very shores of the Lake of Geneva, where, near the mouth of the river, on both banks of the valley, the ancient moraines may be traced to this day, thousands of feet above the level of the water, marking the course the glacier once followed.