The great work of the river has been in excavating the gorge from Lewiston hack to the present position of the cataract. The falls first poured over the edge of the escarpment at Lewis ton and began to dig their way back through hard limestone and sandstone, interbedded with a coherent though softer shale. and for a part of the distance the material was incoherent drift. The process of excavation may he ob served at the falls. The rocks lie in layers and the upper covering of loose drift yields readily to the wash of the waters. Under the drift is hard limestone, called the Niagara limestone, 80 feet in thickness: beneath the limestone lies the softer Niagara shale, with a thickness of 50 feet: then for 35 feet is the Clinton group, an alter nation of limestone, shale, and sandstone, the whole resting upon a bed several hundred feet in thickness of soft sandy shale, which is not known to he interrupted except by a single hard layer of sandstone from 10 to 20 feet thick. These shales and sandstone are called the Medina formation. The hard top layer of limestone projects like a shelf over the edge of the falls so that the water leaps from it and strikes the surface of the pool below. Now and then large blocks of the upper limestone break away and fall into the pool. due doubtless to the erosion of the softer shale beneath, the limestone thus being deprived of its support. Just how the shale is eroded, and how the harder rock beneath it is affected. is in doubt. It is observed in the Cave of the Winds, where visitors may pass behind one of the thinner segments of the falls, that spray and water are constantly dashing against the shale and probably wear it away. The shale is also calcareous, and this element in it being soluble, it is likely that solution has a part in the work of destruction. As the water contains no sediment, the Niagara liver cannot use this agency, as most rivers do, to scow• out its bed; but the broken pieces of rock that fall into the river below the cataract are undoubtedly potent in digging out and deepening the channel. Gov ernment engineers have discovered depths of 200 feet a half mile below the falls, and Gilbert and other geologists assume that the falls are scouring the river bed as deeply now as they did when they were situated farther down the stream. This is occurring in front of the Horse shoe Falls, but not at the American Falls, where the volume of water is comparatively small. The broken rnek here piles up as a talus at the foot of the fall, and upon it the force of the descending water is spent.
The edge of the American Falls is retreating much less rapidly than that of the Horseshoe Falls. The average annual recession on the Amer ican side has been only about a half foot for the past fifty years; but the Horseshoe Falls have receded in fifty-two years from 150 to 230 feet along the western half of its edge. and 270 feet at the apex of its curve. making a recession of from four to six feet a year. If this rate of recession were eonstant, the proof would lie con clusive that the gorge, from the Niagara escarp ment to the falls of to-day, had been excavated in about 7000 years. But the thickness of the resistant Led at the crest of the falls is far from uniform; and there is evidence that at one period after the retreat of the ice the tipper lakes found outlets through other• rivers, and only Lake Erie was drained by the Niagara, whose small volume of water then must have been greatly inferior to that of to-day in its ability to excavate the gorge. The assured fact is that the gorge 6 gradually being cut back toward Lake Erie.
About a half mile above the brink of the falls, Goat Island divides the river into two unequal streams, the one on the American side being comparatively shallow and narrow, and discharging over the American Falls, while most of the river swings around to the left of Goat Island and diseharges over the Horseshoe or Canadian Falls. The resemblance of the outline of these falls to a horseshoe has been destroyed by the more rapid recession of the central part of the cataract edge. The American Falls are 1000 feet wide, and the water is very shallow as it plunges over the edge. filling 167 feet. The have a total width of :1010 feet, measured along the curve, or 1230 across the ehord. a maximum estimated depth of 20 feet.
and a vertien1 height of 158 feet. Att the water is derived from the immense reservoirs of the lakes, there is little variation in the quantity, the differences in volume depending not so pinch upon precipitation as upon the strong winds which slightly retard or accelerate the movement of the surface waters of Lake Erie to the mouth of the river. The normal flow pouring over the cataract is about 500.000 tons a minute.
The falls, being one of the great scenic attrac tions of the world, are visited every year by many thousands of tourists. From the time when Father Hennepin discovered them in 1678. and wildly estimated that they were over 501) feet in height, they have never been adequately de scribed. A realizing sense of the grandeur of this prodigious green flood pouring into an abyss where it is half lost in the masses of ascending mist can be obtained only by personal observa tion. Sightseeing has been greatly facilitated, and visitors protected from imposition since 1885, by the conversion of the land on both sides of the falls into public parks. The New York State Reservation contains 107 acres, and the Queen Victoria Niagara Falls Park on the Canadian side 154 acres. Since these banks became Gov ernment properties, the mean industrial struc tures that marred them have been torn down, and the wonderful spectacle may now be enjoyed at leisure from shady avenues, artificial plat forms, and other advantageous points of view. Trains on the Canadian side wait for a few minutes to give the passengers a glimpse of the vast sheet of water curving over the horseshoe Falls. An electric trolley line has been built through the gorge along the brink of the river on the American side and connects by the Queens town bridge with the electric line skirting the Canadian heights along the gorge and extending past the Horseshoe Falls to Chippawa; a railroad also skirts the United States edge of the. gorge, so that visitors may see its entire length and take in the terrific features of the rapids and the whirlpool. Alany visitors enter the Cave of the Winds. approach the falls on the steamer Maid of the Mist, or enjoy the superb general view from the middle of the upper arch bridge or the high terrace below the Horseshoe Falls on the Canadian side. Several days are re quired even for a cursory examination of all the attractions of the place. The bridge thrown across the river a little below the falls was long regarded as a wonder of engineering. This sus pension bridge for pedestrians and carriages, built of steel about 250 yards below the American Falls, had a span of 821 feet. It lies been re plaeol by an arch bridge. The cantilever•, 910 feet long, spanning the gorge some distance above the Whirlpool, was the first bridge of the kind to be built in America; the railroad steel arch bridge, :300 feet below the cantilever, has a car riageway below the track.
It is only in recent years that important attempts have been made to utilize the energy of Niagara Falls for industrial purposes. The largest plant is that of a power company which generates electricity by leading water through a canal from above the falls to a wheel pit in which are turbines. the water discharging through a tunnel into the river below the falls. :Many in dustries at the falls are using the electricity, and Buffalo. 22 miles distant. takes it for its city railroads and other power purposes. Over three•fourths of the power generated, however, is consumed in the neighborhood of the falls.
BIBLIOGRAPHY. Holley, History of the Falls Bibliography. Holley, History of the Falls of Niagara (New York, 1882) ; Harrison, 7'he Condition of Niagara Falls (ib., 1882) ; Gil bert, "The History of the Niagara River," in ;.:inithsonian Report for 1890 (Washington) ; id., Niagara Falls and Their History (New York, 1895) ; The Niagara Book, by several authors (Buffalo, 1S93); Grabau, Guide to the Geology and Paleontology of Niagara (New York, 1901) ; also Kibbe's account of the various surveys and maps of the falls in the Seventh Annual Report of the commissioners of the New York State Reservation at Niagara (Albany, 1891).