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 
when 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 canons 
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 
