BEAVERS AND BEAVER DAMS.

Press, Volume XLV, Issue 7141, 31 August 1888, Page 3

BEAVERS AND BEAVER DAMS.

The beaver data is a kind of natural ock, subserving a similar purpose, i. c., seeping the water at the requisite level, so as to form a pond out of the stream, in tvhich they may build lodges on the islands, jr on the banks. Beavers knew how to make dams for their purposes centuries before man knew how to build locks or mill dams. They first of all construct a bank across the stream at its bottom, made of mud, brushwood and stones — some very large—which they fetch from bhe land, carrying them in their forepaws against the chest, and walking on their tiind legs; these they sink, and place among the mud, &c.; with branches and logs they further strengthen the bank, gradually raising ib to the level of the stream, adding a great deal of mud, and more stones and logs, until a firm,tthiefk f 3olid dam is made right across the stream, md a pond is formed above. This is called bhe solid bank dam, and is built in broad and deep streams with vertical banks, where the body of water is great, and often rushes with considerable force and 3peed. These dams are often strong enough to support the weight of any horse and rider who may cross them. I* the stream be very rapid and strong, they are built in an arc of a circle, with the convexity towards the flow of stream, so as to resist the force of the water. If the stream be steady, or sluggish, they find that a dam running straight across, with no convexity, is sufficient, and build it accordingly. They sometimes build dams 200 or 300 yards long, though usually they are shorter than this; the thickness varies from 6to 12 feet! The other kind of dam is the stick dam, consisting of sticks and poles interlaced, on the lower side, and the same mixed with mud, &c, on the upper side. This sort is built in slowly running water. In the stick-dam the water drains through it along its entire length, whereas in the solid kind it flows through a single furrow at the top, left by the builders, undoubtedly, for this very nnrpose. They widen or narrow this furrow according to the force of the water. From time to time fresh material is placed on the lower face of the dam to repair it and keep it strong. The water level is kept above the lodge-entrances, but below the lodge-floors. Sometimes two dams are built, one lower down the stream, so as to lessen the destructive force of the water against the upper one. At the bottom of the pond, above the dams, are stored the branches as before described, and in winter these are carried up the inclined plane entrances into the lodaes, the bark stripped off and used for food, the branches taken down again and employed to strengthen the dam; thus both bark and wood are used each for its own purpose. To keep the store of branches safe, they fasten them among the logs and other materials at the base of the dam. It will be easily seen that Beaver can go to and from storehouse or lodge unseen by man, and unaffected by any frozen surface of water. The same may be said of the journeys to or from the burrows. If the lodges are broken up by trappers, th e colony take to these burrows, but very often fall an easy prey to the hunter even there. In order to procure wood from trees some distance inland, these ammah construct a regular system of canals and dams. Mr Morgan gives one case of a canal extending for 509 feet, with three dams en route, each section of the canal being, of course, on a higher level as the journey inward was made, and each dam stretching farther on either side of the canal so as to collect a larger quantity of water from the country around. Down these canals and over the dams the branches are gradually carried to the nond From the discoveries of Agaesiz in the peatbogs of America, it is pretty well ascertained that some beaver works have been in progress for centuries, and that tracks once well wooded have been gradually covered with water by the continuous work of generations oi beavers. — Woraley Bension.