NIAGARA. 149 



lar plate of marble, nearly half an inch thick, open work of 

 most intricate and elaborate description has been executed. 

 It would probably take many days to perform this work by 

 any ordinary process; with the sand-blast it was accom- 

 plished in an hour. So much for the strength of the blast; 

 its delicacy is illustrated by this beautiful example of line 

 engraving, etched on glass by means of the blast. 



This power of erosion, so strikingly displayed when sand 

 is urged by air, renders us better able to conceive its action 

 w lien urged by water. The erosive power of a river is 

 vastly augmented by the solid matter carried along with it. 

 Sand or pebbles, caught in a river vortex, can wear away 

 the hardest rock; " potholes" 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 of Handeck has been 

 thus cut out. Such waterfalls were once frequent in the val- 

 leys 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 Engadin, there is such a case; a 

 hard gneiss being there 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 part dis- 

 solved; but added to this we had the action of the sand 

 and gravel carried along by the water, which, on striking 

 the rock, chipped it away like the particles of the sand- 

 blast. Thus, by solution and mechanical erosion, the 

 great chasm of the Finsteraarschlucht was formed. It is 

 demonstrable that the water which flows at the bottoms of 

 such deep fissures once flowed at the level of their present 

 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 cafions 

 of western America, no other cause is needed than the in- 

 tegration of effects individually infinitesimal. 



And now we come to Niagara. Soon after Europeans 

 had taken possession of the country, the conviction appears 



