Rivers as chief results of Circulation of Water-Zone of Con- stant Evaporation-Condensation and precipitation effected in various ways-Classification of Rivers, as (A) perennial, fed by springs, lakes, peat-mosses or glaciers, and (B) inter- WHAT RIVERS HAVE DONE IN THE PAST. Rivers as agents of Erosion-Waterfalls, Mountain-gorges, Cañons of the Rocky Mountains-Stupendous amount of denuda- tion-Rivers as agents of transport and redeposition— Mountain Course-Highest Waterfalls-Account of Yo-semité and Gavarnie-Middle Course-Niagara and Zambesi- Beauty of landscape-Lower Course-Estuary has a charm PAGE RIVERS IN THEIR RELATION TO HISTORY. Egypt and the Nile-Cities of Mesopotamia-Pre-historic conquest of the valleys of Indus and Ganges-China-Rivers identified SUPERSTITIONS CONNECTED WITH RIVERS. From Homer to Pliny-Alpheus-Shelley-Sabrina, as treated by RIVERS OF FABLE-LAND AND ALLEGORY. Ocean-stream-The five rivers of the Greek Hades-Styx, at first the actual stream of Arcadia, afterwards associated with the Dead-Later Greek beliefs probably borrowed from funeral ceremonies of Egyptians; hence, Charon and the Boat, Cerberus, &c.-Lethe much later, and arose from speculation about transmigration of souls-Treatment of the ANIMAL AND VEGETABLE LIFE OF RIVERS. Most striking in Tropics-Hippopotamus, Crocodile; well de- scribed in Book of Job-Turtles- Birds-Fish-Water- lilies, and other river-plants, their great beauty-Paper-reed RIVERS AS AFFECTED BY HUMAN INDUSTRI Periodical Rise of Tropical Rivers-Embankments-Canals-Deep- Usually very simple, and of uniform meaning in different FROM SOURCE TO SEA. CHAPTER I. WHAT RIVERS ARE. By ceaseless action all that is subsists. That Nature rides upon, maintains her health, Her beauty, her fertility. She dreads An instant's pause, and lives but while she moves. -Cowper's Task, book i. As travellers approach the city of Rome, they are always struck with astonishment at the long lines of arches which cross the desolate Campagna. These colossal remains are what time and neglect have left of the many aqueducts of the ancient Romans. By their means copious streams were poured into the city from the spurs of the Apennines, flowing at one time in tunnels cut through the solid rock, at another in well-aired conduits carried across ravine or plain on double and treble rows of arches. If all the written records of Rome had perished, if her very name were lost, intelligent observers would easily infer the original purpose and office of these majestic ruins. In our globe, taken as a whole, there exist arrangements almost as obvious, the design of which is to supply the world with fresh water. They are, however, so far more wonderful than the aqueducts of the Romans, as their operation extends from Pole to Pole, is unceasing and incapable of serious derangement, and is brought about by blind unintelligent forces working in obedience to a Divine Plan. These arrangements are known collectively as the Circulation of Water. To this great system belong the refreshing dews of night, the flying mists of high mountains, the ever-shifting clouds, the gentle showers, the storms of rain and hail and snow that drench the earth, the fountains, lakes, and rivers that add so much to its beauty, the creeping glaciers of the Alps, the fantastic icebergs of Polar seas. All are but forms of water as it passes through its never-ending round of changes in its journey from the Sea to the Land, and from the Land to the Sea. In this great system Rivers are prominent and important links. They may be said, indeed, to be its most striking results, the most direct channels by which the water condensed from the air is sent back again to its original source. How this is done will be the subject of our first chapter; in other words, what Rivers are at the present day. But as incidentally they do a good deal of other work as well, which in the slow process of time has produced wonderful effects on the face of the earth, we shall devote the second chapter to Rivers as agents of geological change, or what Rivers have done in the past. Evaporation. If water is exposed in a dish, it will in time disappear, more or less rapidly according to the warmth and dryness of the surrounding atmosphere. What becomes of this water? It is evaporated, or passes into the state of invisible vapour, and is then absorbed by the air. Many experiments have shown that warm air can absorb and retain in the gaseous form much more water than cold; that after absorbing the moisture it is much lighter than before; and that air thus saturated, if suddenly chilled, parts with the vapour which it can no longer hold. Evaporation is almost always going on under ordinary conditions from every watersurface on the globe, and even from ice and snow. Though it takes place more actively under direct sunshine and a drying wind, it is not entirely interrupted by cold or darkness. |