Lowell, Mass., how the Old Men of the Mountain helped build it, 34 McCloud River, why it is born half grown, 73 Maine, advance of the sea upon its coasts, 219 Mammoth, art note on, from the "Cavemen's Diary," 22; ancient members of the elephant family that wore underclothes, 24 Manchester, Mass., how the Old Men of the Mountain built its falls, 34 Marble, how a New York City dike helps tell how marble is made, 97; what the fossils have to say, 100; how it is quarried, 103; the mysteries in marble walls, 235; when marble flows, 238; the cloud effects in marble, 239; how marble tells of earthquakes and other exciting things, 239 Mars (planet), 6 Meanders, engineering work of wandering rivers, 81; meanders and the making of natural bridges, 83 Mediterranean Sea, its connection with the making of the Alps, 136 Mercury (planet), 6 Metamorphism (defined), 98 Miller, Hugh, how he found a fish inside of a stone and so found Hugh Miller, 159 Mississippi River, how the Old Men of the Mountain pushed it about, 30; how you can jump across it, 69; the mountains of soil it carries into the sea, 84 Mississippi River System (map), 67 Mississippi Valley, when it was at the bottom of a mediterranean sea, 10; why the sea went away, 138 Missouri River, how it was pieced together and pushed about in the Ice Age, 29 Mohawk River, why it grew taller as it grew older, 72 Molecules, their relations to atoms and electrons, 109 Moraines, how the glaciers take them on their backs, 56 Moulins, the "mills" of the glaciers and how they are made, 55