358 



FALLS OF NIAGARA. 



[Ch. XV. 



of the lava, two water-falls occur at Passo Manzanelli, each 

 about six feet in height. Here the chasm (b, fig. 21) is 

 about forty feet deep, and only fifty broad. 



The sand and pebbles in the river-bed consist chiefly of a 

 brown quartzose sandstone, derived from the upper country ; 

 but the materials of the volcanic rock itself must have greatly 

 assisted the attrition. This river, like the Caltabiano on the 

 eastern side of Etna, has not yet cut down to the ancient bed 

 of which it was dispossessed, and of which the probable 

 position is indicated in the above diagram (c, fig. 21). 



On entering the narrow ravine where the water foams 

 down the two cataracts, we are entirely shut out from all 

 view of the surrounding country; and a geologist who is 

 accustomed to associate the characteristic features of the 

 landscape with the relative age of certain rocks, can scarcely 



from 



scene m some 



The ex- 



ternal forms of the hard blue lava are as massive as any of 

 the oldest trap-rocks of Scotland. The solid surface is in 



almost 



lm 



air of antiquity, which greatly heightens the delusion. But 

 the moment we re-ascend the cliff the spell is broken ; for 

 we scarcely recede a few paces, before the ravine and river 

 disappear, and we stand on the black and rugged surface of a 

 vast current of lava, which seems unbroken, and which we 

 can trace up nearly to the distant summit of that majestic 

 cone which Pindar called the ' pillar of heaven/ and which 

 still continues to send forth a fleecy wreath of vapour, re- 



minding 



b> 



earn 



now described may present themselves to future observers. 



Falls of Niagara, — The falls of Niagara afford a magnifi- 

 cent example of the progressive excavation of a deep valley 

 in solid rock. That river flows over an elevated table-land, 

 in which the basin of Lake Erie forms a depression. Where 

 the river issues from the lake, it is nearly a mile in width, 

 and 330 feet above Lake Ontario, which is about thirty miles 



distant. 



miles 



