In the West beaver are peculiarly useful at stream-sources, where their ponds store flood waters that may later be used for stock water or for irrigation purposes. There are a number of localities in New Mexico, South Dakota, and elsewhere in the West where beaver receive the utmost protection and encouragement from ranchers, whose herds are benefited by water conveniently stored in beaver ponds. A few power companies in the country have commenced to stock with beaver the watersheds which supply them with water. They do this because they realize that countless small ponds or reservoirs are certain to be constructed by these little conservationists. Running water dissolves and erodes away the earthy materials with which it comes in contact. The presence of a beaver pond and dam across a stream's highway prevents the wearing and the carrying away of material. They not only prevent erosion or wearing away, but they take soil and sediment from the water which comes to them and thus cause an upbuilding. Hence the presence of beaver ponds along streams causes an accumulation of sediment and soil. In time these fill rocky channels and cañons, widen and lengthen valleys, and thus extend the productive area of the earth. Beaver ponds are settling-basins, and in them are deposited the heavier matter brought in by the stream. In time the pond is filled, and if the beaver do not raise the height of the dam, the accumulated earthy matter becomes covered with flowers or forests. On the headwaters of the Arkansas River in Colorado some placer miners found gold in the sediment of an inhabited beaver pond. In washing out the deposit of the pond they broke into an enormous amount of loose material beneath, that apparently had been piled in there by glacial action. This material, when removed, was found to have been resting in an ancient beaver pond that was about thirty feet below the one at the surface. [Illustration: WHERE BEAVER FORMERLY LIVED AND SPREAD SOIL] A few centuries ago there were millions of beaver ponds in North America; most of these were long since filled with sediment. Since then, too, countless others have been formed and filled. This soil-saving and soil-spreading still goes ever on wherever there is a beaver pond. Many of the richest tillable lands of New England were formed by the artificial works of the beaver. There are hundreds of valleys in Kansas, Kentucky, Missouri, Illinois, and other States whose rich surface was spread upon them by the activities of beaver through generations. In the Southern States and in the mountains of the West, the numbers of beaver meadows are beyond computation. The aggregate area of rich soil-deposits in the United States for which we are indebted to the beaver is beyond belief, and probably amounts to millions of acres.