10 LAKES OF NORTH AMERICA. 



lake. This lake is variable in area and depth. Sometimes it measures 

 two and one-half miles in l^readth and is about five feet deep ; again, 

 during seasons of unusual drought, it evaporates to dryness. The bar 

 to which it owes its origin rises one hundred and fifty feet above its 

 surface, and under more favorable climatic conditions would retain a lake 

 many square miles in area. The view of the great bar at Stockton and 

 the map of the same locality, presented on Plates 1 and 2, are so graphic 

 and truthful that time need not be taken to describe them. 



Another example of a lake basin formed by a bar crossing the entrance 

 of a lateral valley, is furnished by Lake Annie, near Fort Bidwell, Cali- 

 fornia. The ancient lake on the border of Avhich the bar now retaining 

 Lake Annie was constructed, flooded Surprise valle}', in the northeast 

 corner of California, during Pleistocene times, but is now represented 

 by exceedingly shallow alkaline lakes. Lake Annie is a few hundred 

 yards in diameter, and is kept fresh and sweet by the escape of its surplus 

 waters through the embankment retaining it. 



Perhaps the best of all the examples of the class of water bodies now 

 under consideration, that can be referred to, is Huml)oldt lake, Nevada. 

 This lake occupies a secondary basin in one of the valleys formerly flooded 

 by the Avaters of Lake Lahontan. When the ancient lake was lowered so 

 as to approach extinction, a bar was formed directly across the end of Hum- 

 boldt valley, where it opens out onto the Carsen desert. The waters of 

 Humboldt river were retained by this bar when Lake Lahontan fell so 

 as to leave it dry, and a lake formed above it. The waters escaped across 

 the bar and cut a channel, so as to partially drain the basin above ; but in 

 recent years an artificial drain has been constructed in the opening, and 

 the lake now covers a greater area than it would had the natural con- 

 ditions remained unmodified. A map of the Ixir retaining Humboldt 

 lake, on wdiich much of the history of its origin can be read, is shown in 

 Plate 4.1 



Basins- due to g-lacial ag-encies. — On the surfaces of glaciers, espe- 

 cially on the lower portions of neve regions, there are frequently shallow 

 depressions holding lakes which give variety and an additional charm to 

 the wintry landscapes with which they are surrounded. No case is known 

 in which these lakes are perennial, although they form in the same locali- 

 ties 3'ear after yeai'. They are of little geological interest, for the reason 



1 I. C. Russell, "Quaternary History of Lake Lahontan," U. S. Geol. Surv., Monograph 

 No. n. 



