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Show 178 LAVA EXCAVATED .BY '1'1 IE SIME'l'O· . t The power of running t. ..r the Strne o.- Recent Excava w. nt °Jo mpact roc k l·S exhibited, on a larger water to hollow ou c f Et where a great current t rn base o na, · scale, at the ':es e 0 ) d ding from near the summ1t of lava ( A A, d1 a Oo 'ram o ' escen No.3. flowed to the distance of five or of the great volcano, h~s d the alluvial plain of the Simeto, six miles, and the~· ~~~c e. ers which skirts the base of Etna, the largest of the lCI Ia: nv '1 south of Catania, The lava .c ll . t the sea a lew ml es ' and 1a s m 0 h 1·les above the town of Aderno, d h · er about t ree m entere t el nv pl.e d 1. ts ch anne1 Por some distance, but, cross- 1• • and not on Y occ~ . d f the valley, accumulated there m a ing to the opposlte sl lel o . the year 1603 as the date of Gemme aro g1ves rocky ma.s s. * The appearance of the current clearly p.r oves the er. up. tion ·f the most mo d ern of those of Etna, fo.r 1.t has that lt lS one o db subsequent streams or eJeCtiOns, not been covered or cro~se y ll f small size yet older than 1. 't sur1ace are a o ' f and the o Ives on 1 s 1 In the course therefore, o l d n the same ava. ' fif the natura woo ? he Simeto has eroded a passage from ty about two centuries t . d d in some parts from forty to to several hundred feet WI e, an , fifty feet de:p. throu h is in no part porous or The portiOn of la;a cu; g t homogeneous mass of scoriaceous, but consr~ts ~ h~ ~~~!na~rdinary basalt, containing hard blue rock, somew at Ig ; l . The general declivity of cr~stals of olivine and ta~sy Si::~:r fs not considerable, but, in this part of the bed o t e f th lava two waterfalls consequence of th e une qu. al wha stbe o t sixe f eet in' height. He re occur at Passo Manzanelh, eac . a ~u fort feet deep, and only the chasm (B, diagram No. S.) IS a out y fifty broad. . as to the Some doubts are entertamed Jder "' Quadro Istorico dell' Etna, 1824. ll that it is not one of the o exact date of this curr~nt by others, but a agree streams even of the historical era. l~ALLS OF NIAGARA. 179 The sand and pebbles in the river bed consist chiefly of a brown quartzose sandstone, derived from the upper country; but the matter derived from the volcanic rock itself must have greatly assisted the attrition. This river, like the Caltabianca, has not yet cut down to the ancient bed of which it was dispossessed, and of which we have indicated the probable position in the annexed diagram (c, No. S.) 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 dissuade himself from the belief that he is contemplating a scene in some rocky gorge of a primary district. The external forms of the hard blue lava are as massive as any of the most ancient trap-rocks of Scotland. The solid surface is in some parts smoothed and almost polished by attrition, and covered in others with a white lichen, which imparts to it an air of extreme antiquity, so as greatly to heighten the delusion. But the moment we reascend 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 pillat· of heaven," and which still continues to send forth a fleecy wreath of vapour, reminding us that its fires are not extinct, and that it may again give out a rocky stream, wherein other scenes like that now described may present themselves to future observers. Falls of Niagara.-The falls of Niagara afford a magnificent example of the progressive excavation of a deep valley in solid rock. That river flows from Lake Erie to Lake Ontario, the former lake being three hundred and thirty feet above the latter, and the distance between them being thirty-two miles. On flowing out of the upper lake, the river is almost on a level with its ?anks; so that, if it should rise perpendicularly eight or ten feet, It would lay under water the adjacent flat country of Upper Canada on the West, and of the State of New York on the N2 |