THE LAKE OF GENEVA (the Latin Lacus Lemanus or Lake Léman, also known in the Middle Ages as Lac Losannete or Lake of Lausanne, and as Mer du Rhône or Sea of the Rhone), is the largest of the Swiss lakes, having an area of 578 sq. kil. or 223 sq. miles. Its general form is that of a crescent, the northern shore being almost the arc of a circle, with a radius of 21J miles. The eastern end of the crescent is broad and rounded, while the western tapers towards Geneva. Its maximum breadth, between Morges and Amphion, is 8|- miles. It is divided into two portions, the Great and Little Lake, by the strait of Promonthoux, which is not much more than 2 miles across. The Great Lake is 39 miles long, with a mean breadth of 6 miles, and the Little or Western Lake is 14 miles long, with a mean breadth of rather more than 2 miles. The bottom of the larger basin forms a wide valley, which gradually deepens from 200 to 325 feet at the foot of the slopes to a maximum of 1095 feet, which it attains between Ouchy and Évian. The mean level of the surface of the lake is 1230 feet above the level of the sea. According to the elaborate soundings made in 1873 by M. Gosset, engineer of the Federal Topographic Depart-ment, the bottom is remarkably free from inequalities, almost all traces of rocks, erratic blocks, or moraines, having been covered over by a regular bed of extremely fine argillo-calcareous mud, which can be moulded and baked like potter's clay. Between the basin of the Great Lake and that of the Little Lake there runs a ridge or bar not very strongly marked, 200 feet from the surface. The maximum depth of the lesser basin is only 71 metres or 233 feet. The bottom is apparently level, but it presents numerous erratic blocks, and in one place rises to a con-siderable eminence, known to the Genevese fishers as the Hauts Monts. The unusual blueness of the waters of the Leman has long been remarked. According to M. Forel, the transparency is very much greater in winter than summer, the extreme limit of visibility of a white disk on an average for the seven winter months from October to April being 41 feet, and for the five summer months 21-6. This arises from the thermal stratification of the water keeping in suspension a greater quantity of dust and organic particles during summer. It is generally in August that the level of the lake reaches its highest limit, between 4 and 5 feet on an average above its lowest limit, which is usually reached in March. Besides this seasonal change, due to differences of influx and removal of water, several disturbances of level of a less obvious kind have attracted the attention of the Swiss physicists. Most remarkable are the seiches, or " movements of steady o uninodal oscillation," in which the whole mass of water in the lake rhythmically swings from shore to shore. According to M. Forel, there are both longitudinal and transverse seiches. Their effect is most distinctly seen at Geneva, where they sometimes raise the level of the water from 4 to 5 feet. They are not improbably due to several distinct causes, but the most efficient would appear to be a difference of barometric pressure in different parts of the
Lake of Geneva.
lake. In the eastern portion of the lake there is an irregular but violent current during spring and autumn, called Lardeyre or La Diere, which is supposed to be due to subterranean affluents. The principal winds are the Bise from the north-east, the stormy Bornand that rushes from the ravines of Savoy, and the dry south wind, known as the Sechard. Less use is made of the lake as a means of communication since the opening of the railway along the Swiss shore, but the lateen sails of the minor craft still brighten the landscape, and an excellent steam service is maintained by a company formed in 1873. The first steamboat, the "William Tell," was introduced on the lake in 1823; and the first saloon steamboat, the "Mont Blanc," dates only from 1876.
3 M. Forel's numerous studies on the subject will be found in the Bibliotheque Universelle, and the Bulletin de la soc. vaud. (Lausanne).
The Lake of Geneva is not so rich in fish as many of the smaller lakes of Switzerland. Comparatively small success has attended the attempts of Professor Chavannes of Lausanne to introduce the salmon, which, like many other fishes, finds the Perte du Rhone a barrier between the sea and the lake. The " fera " (Coregonus /era) is economically the most important species. In the mud at the bottom of the lake there exists an interesting fauna, of about 40 species, mainly belonging to the lower orders. Several of the species, as Gammarus ccecus, are found 1000 feet below the surface, in the reign of perpetual darkness. Two species of gasteropods of the genus Limnceus are worthy of special note as possessing developed lung3, though they live at a depth of from 150 to 300 feet.
See Rodolphe Rey, Geneve et les rives du Leman, 3d ed. (Geneva, 1875); Egli, Taschenbuch Schweizerisehen statistics (Zurich, 1875); Herbst, Der Genfer See und seine Umgebung (Weimar, 1877).
Further details on the conformation of the lake will be found in De la Beche's letter to Professor Pictet, published in Bibliothèque Universelle: Sciences et Arts, t. xii., 1817 ; in M. Gosset's Carte Ilydrogr. du Lac Léman, issued as part of the Topog. Atlas der Schweiz, and described in Bibl. Un. (Sci. et Arts), t. Ih., 1875, and in a, Note sur la Carte du Lac, by Ed. Pictet, in the same number.
"Étdes sur les variations de la transparence des eaux du lac
Léman," in Bibl. Un. (Se. et Arts), 1877.
According to G. Lunel, whose Histoire naturelle des poissons du bassin du Leman, (Geneva, 1874) has superseded the valuable memoir of Professor Jurine in the Memoires de la SoeiUU de physique, tome iii. (1825), there are 21 species:Perca fluviatilis, L.; Cottus gobio, L.; Lota vulgaris, Cuv.; Cyprinus carpio, L.; Cyprinopsis auratus, L.: Tinea vulgaris, Cuv.; Gobio fluviatilis, Cuv.; Albumus lucidus, Heckel; Alb. bipunctatus, L.; Scardinius erythrophtlialmus, Bonap.; Leuciscus rutilus, L.; Squalius cephalus, Bonap.; Phoxinus Icevis, Ag.; Cobitis barbatula, Lin.; Coregonus fera, Jurine ; Coregonus hiemalis, Jurine; Thymallus vulgaris, Nilsson ; Salmo umbla, L.; Trulta variabilis, G. L.; Esox lucius, L.; Anguilla vulgaris, Fleming.
M. Forel's numerous studies on the subject will be found in the Bibliotheque Universelle, and the Bulletin de la soc. vaud. (Lausanne).