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PHYSICAL GEOGRAPHY. 



slower its motion, the farther the tide will penetrate ; whereas a narrow and sinuous 

 course, and a great velocity, offer obstructions to its progress. The tide of the Atlantic 

 is perceived four hundred miles along the course of the Amazon, and that of the German 

 Ocean extends about seventy miles up the Thames. Important facilities are afforded to 

 the navigation of many rivers by this circumstance, for they are only accessible to vessels 

 of large burden at high water. The rapid of Richelieu, on the St. Lawrence, where the 

 river contracts, and has its course obstructed by rocks, impedes the navigation between 

 Montreal and Quebec, except at high tide, when the water rises fifteen or eighteen feet, 

 and the rapid entirely disappears. A semi-annual or an annual rise alone distinguishes 

 the rivers of inter-tropical regions and of countries bordering on the torrid zone. The 

 semi-annual rise is a feature of those rivers which drain high mountain ranges, and pro- 

 ceeds from the two independent causes, of the melting of the snows in spring or summer, 

 and the great seasonal rains to which such districts are subject. The rivers which have 

 only one annual rise are influenced by the latter cause alone, or by the two acting coin- 

 cidently, and producing a grand periodical flood. The Tigris rises twice in the year - 

 first, and most remarkably, in April, in consequence of the melting of the snows in the 

 mountains of Armenia ; and secondly, in November, through an accession from the pe- 

 riodical rains. The Mississippi likewise is subject to two rises in the year one about 

 January, occasioned by the periodical rains that fall towards the lower part of its course ; 

 but the grand flood commences in March, and continues till June, proceeding from the 

 melting of the ice in the upper part of the continent, where the Missouri and other tribu- 

 tary streams have their origin. A very striking spectacle is exhibited by this river in 

 the season of inundation. It rises from forty to fifty feet in some parts of its course, 

 and is from thirty to a hundred miles wide, all overshaded with forest, except the interior 

 stripe consisting of its bed. The water stands among the trees, from ten to fifteen feet 

 in height, and the appearance is exactly that of a forest rising from a lake, with its 

 waters in rapid motion. For the protection of the cultivated lands, and to prevent their 

 conversion into permanent swamps, an embankment, called the Lessee, has been raised, 

 which extends two hundred miles on the eastern shore of the river, and three hundred on 

 the western. In Asia, the Ganges, Indus, and Euphrates exhibit inundations upon a 

 similarly great scale. The Euphrates slightly increases in January, but the grand flood 

 begins soon after the middle of March. It attains its height about the 20th of May, 

 after which it falls rapidly till June. The decrease then proceeds gradually until the 

 middle of November, when the stream is at its lowest. The rise of the water at Anah, 

 above the site of ancient Babylon, occasionally amounts to eighteen feet, sometimes 

 entering that town, running with a velocity exceeding five miles an hour. The moment 

 that the waters of the river recede, the rice and grain crops are sown in the marshes, and 

 villages of slightly made reed cottages are reared in their neighbourhood. These last, in 

 consequence of being suffered to remain too long, are often surprised by the returning 

 inundation, and it is no uncommon spectacle for their occupants to be seen following the 

 floating villages in canoes, for the purpose of recovering their property. But of all 

 inundations, that of the Nile, if not the most extensive, is the most regular, and has 

 become the most celebrated, from the knowledge of it going back to the earliest periods 

 to which history recurs. The rise of the river commences about the time of the summer 

 solstice, attains its maximum height at the autumnal equinox, remains stationary for 

 some days, and then gradually diminishes till the time of the winter solstice. The 

 ancients, unacquainted with the climate of the interior country from which it descends, 

 and not caring in general to inquire for physical causes, possessing also a very limited 

 knowledge of terrestrial phenomena, deemed the annual overflow of the Nile a unique 

 event, and attributed it to the special interference of a supernatural power. Lucretius, 



