Page:Popular Science Monthly Volume 3.djvu/233

Rh can wear away the hardest rock; "pot-holes" and deep cylindrical shafts being thus produced. An extraordinary instance of this kind of erosion is to be seen in the Val Tournanche, above the village of this name. The gorge at Handeck has been thus cat out. Such water-falls were once frequent in the valleys of Switzerland; for hardly any valley is without one or more transverse barriers of resisting material, over which the river flowing through the valley once fell as a cataract. Near Pontresina, in the Engadine, there is such a case, the hard gneiss being now worn away to form a gorge through which the river from the Morteratsch Glacier rushes. The barrier of the Kirchet, above Meyringen, is also a case in point. Behind it was a lake, derived from the glacier of the Aar, and over the barrier the lake poured its excess of water. Here the rock, being limestone, was in great part dissolved, but, added to this, we had the action of the solid particles carried along by the water, each of which, as it struck the rock, chipped it away like the particles of the sand-blast. Thus, by solution and mechanical erosion, the great chasm of the Fensteraarschlucht was formed. It is demonstrable that the water which flows at the bottoms of such deep fissures once flowed at the level of what is now their edges, and tumbled down the lower faces of the barriers. Almost every valley in Switzerland furnishes examples of this kind; the untenable hypothesis of earthquakes, once so readily resorted to in accounting for these gorges, being now, for the most part, abandoned. To produce the canons of Western America, no other cause is needed than the integration of effects individually infinitesimal.

And now we come to Niagara. Soon after Europeans had taken possession of the country, the conviction appears to have arisen that the deep channel of the river Niagara below the Falls had been excavated by the cataract. In Mr. Bakewell's "Introduction to Geology," the prevalence of this belief has been referred to: it is expressed thus by Prof. Joseph Henry in the Transactions of the Albany Institute: "In viewing the position of the Falls, and the features of the country round, it is impossible not to be impressed with the idea that this great natural race-way has been formed by the continued action of the irresistible Niagara, and that the Falls, beginning at Lewiston, have, in the course of ages, worn back the rocky strata to their present site." The same view is advocated by Mr. Hall, by Sir Charles Lyell, by M. Agassiz, by Prof. Ramsay—indeed, by almost all of those who have inspected the place.

A connected image of the origin and progress of the fall is easily obtained. Walking northward from the village of Niagara Falls by the side of the river, we have, to our left, the deep and comparatively narrow gorge through which the Niagara flows. The bounding cliffs of this gorge are from 300 to 350 feet high. We reach the whirlpool, trend to the northeast, and, after a little time, gradually resume our