In this and other ways the water works its way back in a surprising manner.  The Isle of Wight gives us some good instances of this; Alum Bay Chine and the celebrated Blackgang Chine have been entirely cut out by waterfalls.  But the best know and most remarkable example is the Niagara Falls, in America.  Here, the River Niagara first wanders through a flat country, and then reaches the great Lake Erie in a hollow of the plain.  After that, it flows gently down for about fifteen miles, and then the slope becomes greater and it rushes on to the Falls of Niagara.  These falls are not nearly so high as many people imagine, being only 165 feet, or about half the height of St. Paul’s Cathedral, but they are 2700 feet or nearly half-a-mile wide, and no less than 670,000 tons of water fall over them every minute, making magnificent clouds of spray.

Sir Charles Lyell, when he was at Niagara, came to the conclusion that, taking one year with another, these falls eat back the cliff at the rate of about one foot a year, as you can easily imagine they would do, when you think with what force the water must dash against the bottom of the falls.  In this way a deep cleft has been cut right back from Queenstown for a distance of seven miles, to the place where the falls are now.  This helps us a little to understand how very slowly and gradually water cuts its way; for if a foot a year is about the average of the waste of the rock, it will have taken more than thirty-five thousand years for that channel of seven miles to be made.

But even this chasm cut by the falls of Niagara is nothing compared with the canyons of Colarado.  Canyon is a Spanish word for a rocky gorge, and these gorges are indeed so grand, that if we had not seen in other places what water can do, we should never have been able to believe that it could have cut out these gigantic chasms.  For more than three hundred miles the River Colorado, coming down from the Rocky Mountains, has eaten its way through a country made of granite and hard beds of limestone and sandstone, and it has cut down straight through these rocks, leaving walls from half-a-mile to a mile high, standing straight up from it.  The cliffs of the Great Canyon, as it is called, stretch up for more than a mile above the river which flows in the gorge below!  Fancy yourselves for a moment in a boat on this river, as shown in Figure 27, and looking up at these gigantic walls of rock towering above you.  Even half-way up them, a man, if he could get there, would be so small you could not see him without a telescope; while the opening at the top between the two walls would seem so narrow at such an immense distance that the sky above would have the appearance of nothing more than a narrow streak of blue.  Yet these huge chasms have not been made by any violent breaking apart of the rocks or convulsion of an earthquake.  No, they have been gradually, silently, and steadily cut through by the river which now glides quietly in the wider chasms, or rushes rapidly through the narrow gorges at their feet.