ice would descend with crushing force on these rocks. The smaller ones would be broken, pulverized, and swept down-stream, the channel for the water would be enlarged gradually, and the larger masses thus partially undermined. Then the spray and dashing water would freeze and the ice accumulate upon them until they were toppled over. Then the falling ice would recommence its chipping labors, and with every piece of ice knocked off, a portion of the rock would go with it. Finally, as the cold continued, the master force, the mightiest of mechanical powers, would be brought into action. The vast quantities of ice pouring over the precipice would freeze together, agglomerate, and form an ice-bridge. The roof being formed, the succeeding cakes of ice would be drawn under, and, raising it, be frozen to it. This process goes on. Every piece of rock above and below the surface is embraced in a relentless icy grip. Millions of tons are frozen fast together. The water and ice continue to plunge over the precipice. The principle of the hydrostatic press is made effective. Then commences a crushing and grinding process which is perfectly terrific. Under the resistless pressure brought to bear upon it, the huge mass moves half an inch in one direction, and an hundred cubic feet of rock are crushed to powder. There is a pause. Then again the immense structure moves half an inch another way, and once more the crumbling atoms attest its awful power. This goes on for weeks continuously. Finally the temperature changes. The sunlight becomes potent; the ice ceases to form; the warm rays loosen the grip of the ice-bridge along the borders of the chasm below. The water becomes more abundant; the bridge rises, bringing in its icy grasp whatever it had attached itself to beneath; it breaks up into masses of different dimensions: each mass starts downward with the growing current, breaking down or filing off everything with which it comes in contact. Fearful sounds come up from the hidden depths, from the mills which are slowly pulverizing the massive rock. The smaller bits and finer particles, after filling the interstices between the larger rocks in the bottom of the chasm, are borne lakeward. The heavier portions make a part of the journey this year; they will make another part next year, and another the next, being constantly disintegrated and pulverized. This work has been going on for many centuries. The result is seen in the vast bar of unknown depth which is spread over the bottom of Lake Ontario around the mouth of the river. On the inner side of the bar the water is from sixty to eighty feet deep, on the bar it is twenty-five feet deep, and outside of it in the lake it reaches a depth of six hundred feet. [Illustration: GREAT ICICLES UNDER THE AMERICAN FALL]