ORIGIN OF LAKE HAS INS. 9 



The overloaded streams from oLu-iers also form levees, in much the 

 same manner as in the case of more mature streams. These embank- 

 ments are apt to be formed of both coarse and tine material, and sometimes 

 enclose low areas, so as to obstruct their drainage and give origin to lakes 

 and ponds. Young streams, on account of the amount of debris con- 

 tributed to them, tlius in some instances, simulate to a certain degree 

 the behavior of more mature rivers. Small lakes of the class here referred 

 to occur about the southern border of the Malaspina glacier, .Vlaska. 



b. Basi)ii< formciJ hi/ traves and cun'cttts. — Basins are frecpiently 

 formed along the ocean's shore and on the border of lakes, where sand 

 and gravel bars have been built across the entrances of bays, or extend 

 from headland to headland so as to cut off a curve of the shore. Xumer- 

 ous examples of water bodies that have l)een isolated in tliis way, occur 

 along the Atlantic coast and about the shore of the Laurentian lakes. 

 The history of some of these secondary lakes may Ije easily read from 

 the exceedingly A'aluable series of charts published by the U. S. Coast 

 and Geodetic Survey and by the U. S. Lake Survey. It frequentl}' hap- 

 pens that lakes separated from the ocean by narrow sand bars, are fresh. 

 This is due to the fact that the movement of Avater through the shore 

 deposits is from the land seaward, and the originally saline waters in such 

 enclosures have been flooded out. The seaward flow of underground 

 water also explains why fresh water may be obtained in wells on sand 

 bars of the character here referred to. 



Besides living examples of the class of lakes here considered, there 

 are basins of a similar origin still to be seen about the borders of lakes 

 that have ceased to exist. In the Great Basin, and especially on the 

 borders of the valle3's formerly flooded by tlie waters of lakes Bonneville 

 and Lahontan, there are small lakes and enclosed basins not now flooded, 

 which are due to the formation of embankments about the margin of 

 those ancient water bodies. The valleys formerly covered with the 

 water of these great seas to the depth of many hundreds of feet are now 

 for the most part parched and arid, and desert shrul)s cover the em- 

 baid\ments of sand and gravel on which the surf formerly broke. Only 

 a few of tlie secondary basins formed along those ancient shores can be 

 refcrrefl to at this tim(^ 



At the town of Stockton, I'taii, about liftcen mik's south of Great Salt 

 lake, there is an innnense gravel bar, formed near tlie highest stage of 

 Lake Bonneville, which s\v('c[ts comph'ti-ly across tlie cntiance of a valley 

 and retains the waters drainint'' from the southward, so as to form Bush 



