Picture herds of these mammoths huddled together like sheep in dark ravines, and the blinding snow, swept down by the winds, burying them deeper and deeper. That was how they died. You'll notice that they wore their hair long, while the elephants we see in the circuses or at the zoo have hardly any hair at all. This long hair was part of their winter clothing. Under it they wore a close fleece. But this winter was so severe and it lasted so long that even their heavy woollen underwear couldn't save them. Sometimes there would be a thaw, but this was only on the surface and helped turn the snow into ice. And winter piled on winter and on the bodies of the mammoths until they were buried under tons and tons of snow and ice. HOW THE SNOW CHANGED ITSELF INTO ICE You know snow will get solid, like ice, where it is under pressure, and it will make hard cakes and ice balls under your shoes. Well, this snow of the long winter just "packed its own self" (as a small boy might say) into ice. It did this by piling on and piling on. The weight of the snow above and behind, in the spaces between the mountains and in the mountain valleys, pressed with enormous force on the snow below and in front. Then what do you think this ice did? It began to move. And of all the things it did from then on! II. Marvellous Changes in the Old Home Place Did you notice those scratches on my face? The ice did that. But, of course, that's nothing in itself. And, besides, I'm not one to complain, as you know. I only speak of it to show what big things may be back of little ones, how much you can learn from the study of so common a thing as a little pebble. For the very same ice fields that scratched the faces of little pebbles like me deepened the gorges and canyons among the mountains and shaved the crowns of the old ones--Bald Mountain, in the Adirondacks, for example. They carried off good farming soil by the thousands of acres from one place and piled it in another; they shoved the Mississippi River back and forth; in fact, turned many streams out of their courses--some of them the other end to, so that they now flow south where they used to flow north. They took old river systems apart, and with the pieces made new ones--the big Missouri for one. They set Niagara Falls up in business; got all the waterfalls ready that are now turning the wheels of New England factories, and even put in great water storage systems that remind one of the Salt River irrigation works, with their big Roosevelt dam in Arizona, or of the reservoirs which England built in the Nile. Lakes in river systems act as reservoirs, you know, and make them flow more evenly, thus keeping the power of falls more uniform, as in the case of Niagara, and making a uniform depth of water for vessels, as in the case of the St. Lawrence River. The Great Lakes do both of these useful things. [Illustration: _From Norton's "Elements of Geology." By permission of Ginn and Company_