Rivers and Their Mysteries (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 Excerpt: ...dredges or hydraulic power. Where the stream is large and conditions are favorable dredges are employed which dig up vast quantities of gravel and sand from the river bed and banks and pass it over tables, sluices and other machinery where the precious metals or gems are separated from the sand. By handling an enormous amount of material at a very low cost many placers can be worked at a profit by dredges when it would be impossible to make them pay if worked by hand. In other localities, where the streams are too small for dredges or where the country is too rough or conditions are not right, the placers are worked by immense streams of water played upon the banks from giant hose-pipes and huge nozzles known as "monitors" or "giants." These streams cut and tear away the gravel and sand and wash it into huge, sluice-like arrangements with riffles made of railway rails. In this way, vast hillsides and mountains are rapidly cut and washed away and the wealth they hold is given up to man. Very often the water used in these hydraulic mines is brought many miles, for in order to obtain a strong enough stream to cut the gravel a dam must be built many feet above the level of the spot where the work is going on. Thus you see, the rivers not only gather up the wealth of vast areas of land and hoard it ready for man to secure, but in addition, they supply man with the means of obtaining it and so, in still another way, they serve mankind and from their beds furnish incalculable fortunes to help the civilization, the progress and the industry of the world. Chapter VI SOME UNUSUAL RIVERS We usually think of rivers as streams of water rising in some definite spot, flowing across a country and emptying at last into the sea. They may rise among the mo...