In illustration of this point I will refer, in the first place, to that tributary of the Lower Glacier of Grindelwald which descends from the Strahleck. Walking up this tributary we come at length to the base of an ice-fall. Let the observer here leave the ice, and betake himself to either side of the flanking mountain. On attaining a point which commands a view both of the fall and of the glacier below it, an inspection of the glacier will, I imagine, solve to his satisfaction the case of structure now under consideration. It is indeed a grand experiment which Nature here submits to our inspection. The glacier descending from its _neve_ reaches the summit of the cascade, and is broken transversely as it crosses the brow; it afterwards descends the fall in a succession of cliffy ice-ridges with transverse hollows between them. In these latter the broken ice and debris collect, thus partially choking the fissures formed in the first instance. Carrying the eye downwards along the fall, we see, as we approach the base, these sharp ridges toned down; and a little below the base they dwindle into rounded protuberances which sweep in curves quite across the glacier. At the base of the fall the structure begins to appear, feebly at first, but becoming gradually more pronounced, until, at a short distance below the base of the fall, the eye can follow the fine superficial groovings from side to side; while at the same time the ice underneath the surface has become laminated in the most beautiful manner. It is difficult to convey by writing the force of the evidence which the actual observation of this natural experiment places before the mind. The ice at the base of the fall, retarded by the gentler inclination of the valley, has to bear the thrust of the descending mass, the sudden change of inclination producing powerful longitudinal compression. The protuberances are squeezed more closely together, the hollows between them appear to wrinkle up in submission to the pressure--in short, the entire aspect of the glacier suggests the powerful operations of the latter force. At the place where _it_ is exerted the veined structure makes its appearance; and being once formed, it moves downwards, and gives a character to other portions of the glacier which had no share in its formation. [Sidenote: BASE OF CASCADE A "STRUCTURE-MILL."]