638 THE FRESH- WATER LOCHS OF SCOTLAND 
miles into the highlands, thus reaching in total length about 100 
miles, and the width of the valley at the level of the lake is only 
about 4 miles. The lake is over 1100 feet deep, for in several sound- 
ings at that depth Russell found no bottom ; the surface is only 950 
feet above the sea, so that the bottom of the trough is many feet 
below sea-level. The lake has no beach, and there is scarcely a trace 
on the rocks, except at the eastern end, to show that it has altered its 
level, so that it must be of comparatively recent origin, and appears 
to date from the glacial invasion already mentioned. The valley was 
not, however, cut by the glacier which occupied it, but is a stream- 
worn channel, and must at a still earlier period in the earth's history 
have been excavated in the hard granite by the action of water. 
Kiver San Tulare Lake, in the southern part of the valley of California, is 
Joaquin, f^^.j^^j^^ King River ponding back the upper streams of the San 
Joaquin River. The river system is youthful, and the lateral stream, 
gnawing into a lofty slope, sweeps down with it more waste than the 
main stream can carry away. The surplus accumulates as a fan-shaped 
delta, and dams back the water, forming a shallow lake with indefinite 
marshy shores much overgrown with reeds (Spanish tides). It was 
formerly nearly 50 miles in length, but is now practically dry as 
a result of the withdrawal for irrigation purposes of the waters of 
King and Kern Rivers formerly discharging into it. 
Mexico. Lake Chapala, the largest lake in Mexico, is traversed by the 
Rio Lerma, or Rio Grande de Santiago, which flows into the Pacific 
north of San Bias. The lake is in a manner an expansion of the 
river, covering an area of about 1300 square miles, and the maximum 
depth is 98 feet. It is about 80 miles in length by 20 miles in 
width, but fluctuates with the dry and wet seasons. 
The other important lakes of Mexico are connected with inland 
drainage areas, and have been described under that heading. 
Central Lakes Nicaragua and Managua both lie in a depression in the 
America. ^^^^ ^£ ^j^^ State of Nicaragua, separated from the Pacific by the 
continental divide from 12 to about 30 miles in width. The overflow 
from Lake Managua, the smaller and more northerly of the two, is 
carried into Lake Nicaragua, and thence by the San Juan into the 
Caribbean Sea at Grey town. Lake Nicaragua has an area of about 4400 
square miles, is about 110 miles in length by about 40 miles in average 
breadth, with a maximum depth of about 150 feet, and its surface 
varies from 110 feet to 97 feet above sea-level. The lake contains 
several islands, some of which show monuments of an old civilisation, 
and one — the island of Omotepe — is an active volcano. A ship-canal 
