In high northern countries, as in Siberia, the rivers, even the deepest, often become so far frozen that their channels are entirely obstructed. Where, as in the case of these Siberian rivers, the flow is from south to north, it often happens that the spring thaw sets in before the more northern beds of the main stream are released from their bondage of frost. In this case the inundations have to find new paths on either side of the obstructed way. The result is a type of valleys characterized by very irregular and changeable stream beds, the rivers having no chance to organize themselves into the shapely curves which they ordinarily follow. The supply which finds its way to a river is composed, as has been already incidentally noted, in part of the water which courses underground for a greater or less distance before it emerges to the surface, and in part of that which moves directly over the ground. These two shares of water have somewhat different histories. On the share of these two depends the stability of the flow. Where, as in New England and other glaciated countries, the surface of the earth is covered with a thick layer of sand and gravel, which, except when frozen, readily admits the water; the rainfall is to a very great extent absorbed by the earth, and only yielded slowly to the streams. In these cases floods are rare and of no great destructive power. Again, where also the river basin is covered by a dense mantle of forests, the ground beneath which is coated, as is the case in primeval woods, with a layer of decomposing vegetation a foot or more in depth, this spongy mass retains the water even more effectively than the open-textured glacial deposits above referred to. When the woods, however, are removed from such an area, the rain may descend to the streams almost as speedily as it finds its way to the gutters from the house roofs. It thus comes about that all regions, when reduced to tillage, and where the rainfall is enough to maintain a good agriculture, are, except when they have a coating of glacial waste, exceedingly liable to destructive inundations. Unhappily, the risk of river floods is peculiarly great in all the regions of the United States lying much to the east of the Rocky Mountains, except in the basin of the Great Lakes and in the district of New England, where the prevalence of glacial sands and gravels affords the protection which we have noted. Throughout this region the rainfall is heavy, and the larger part of it is apt to come after the ground has become deeply snow-covered. The result is a succession of devastating floods which already are very damaging to the works of man, and promise to become more destructive as time goes on. More than in any other country, we need the protection which forests can give us against these disastrous outgoings of our streams. LAKES.