320 PHYSICAL GEOGRAPHY. 



is called " the raft," the dimensions of which in 1816 amounted to a length of 10 miles, a 

 width of 220 yards, and a depth of 8 feet. This is an island afloat in the bosom of the 

 waters, having externally the appearance of solid land, for green bushes and a variety of 

 beautiful ilowers bloom upon its surface. The age of the raft, at the time when the pre- 

 cedin" 1 dimensions were given, is supposed to have been not more than thirty-eight years, 

 from which some idea may be formed of the immense quantity of drift-wood borne down 

 by the waves of the Mississippi. 



The Swiss lakes exhibit some peculiar and interesting features. That of Zurich 

 presents annually what is called the flowering of its waters. This is the appearance upon 

 the surface of a very minute vegetation. But the lake of Geneva, or Lac Leman, 

 furnishes the most remarkable phenomenon. This is generally considered the finest 

 inland sheet of water in southern Europe. It fills a great cavity in the rocky strata of 

 Switzerland, extending about forty-seven miles in its greatest length, and nine miles in its 

 greatest breadth. High and rugged mountains form its boundary to the east, with more 

 gentle slopes to the west, enriched with corn fields, villas, and vineyards. The turbid 

 and discoloured waters of the Khone are filtered in it, and issue forth beautifully clear and 

 pellucid. Owing to this deposition from the river, the lake has been largely contracted 

 at the point where the stream enters, so that the Roman town, Portus Valesise, which 

 was close to the water's edge, is now separated from it by a tract of land more than a 

 mile and a half in breadth. Among the peculiarities of the lake of Geneva, is that called 

 Seiches, by the people of the neighbourhood. It consists in a sudden rising of the water, 

 in the form of a tidal wave, sometimes to the height of five or six feet in the course of a 

 few hours. A few of the Italian lakes, and some others of the Swiss, are subject to the 

 same great undulatory movement, the cause of which is by no means certain, but con 

 ceived to lie in some local and transient variation of the pressure of the atmosphere. 

 There is another phenomenon of which this lake is the scene, called the Vaudaise. This 

 is the ebullition of its waters, arising perhaps from the escape of subaqueous currents of 

 air or gases. The agitation produced is at times so violent as to render the navigation 

 of the lake dangerous. 



The appearance of tumult upon the surface of lakes without any sensible cause for it, 

 is far from being uncommon, however strange it must seem, to see their waters tossing 

 to and fro, in the calmest weather, when not a twig is stirring in the woods upon their 

 banks. On the 1st of November 1755, without the least apparent cause, agitation seized 

 the before peaceful waters of Loch Lomond, and they suddenly rose against their 

 shores to a perpendicular height of two feet, and then subsided below their ordinary 

 level. This was soon afterwards explained by the coincident occurrence of the earthquake 

 at Lisbon. But Loch Lomond, along with lake Wetter in Sweden, often exhibit great 

 disturbance, the cause of which must lie in themselves, and is probably due to the escape of 

 currents of air from below their bed, though obscurity rests upon the manner of the form 

 ation of this subaqueous and subterranean prison-house of the winds, or upon the opening 

 of its doors. In the winter season, a lake near Boleslaw in Bohemia, which has never 

 been sounded, also exhibits upon its surface the effects of the action of some internal force ; 

 large masses of ice being whirled from it into the air. But of all phenomena of this kind, 

 those which mark the Baikal are the most singular and unaccountable. They give it 

 somewhat of a prophetic character, and would justify incredulity were they not well 

 attested. It is rarely the case that its waters are smooth and calm, but when they are so, 

 vessels upon their surface are often so violently shaken as to make it difficult to stand in 

 them. There is commonly an undulation, which the sailors call kolychen or zyb, which 

 increases previous to a wind arising. This undulation proceeds from the quarter of the 

 wind, and its increase precedes it by about an hour ; but while a moderate wind will be 



