1882.] 
367 
[Davis. 
vastly more enduring. Examples are not numerous; in Auvergne, 
Lac d’Aidat, a small basin, is so enclosed by lava from the 
extinct Puy de la Vache, 1 and the Lac de Chambon was formed 
by the eruption of volcanic cones in its valley. The Sea of 
Tiberias seems held back by a lava stream that entered the val- 
ley of the Jordan from the east. 2 Asia Minor will probably fur- 
nish other examples. 
Lake Assal, at the head of the Gulf of Aden, is shut in by 
a bed of lava containing several deep craters ; it is about seven 
miles long, with a surface depressed by evaporation six hundred 
feet below the adjoining sea-level; its waters are very salt and 
there are salt deposits around it. 3 Owen’s Lake, in Southern 
California, east of the Sierra, and some others in Utah are prob- 
ably enclosed in the same way. 4 Perhaps the group of lakes in 
Northeastern California, drained by the Klamath, are of this 
origin, as the region is one of great lava-flows. 
This species might be subdivided like the Ice Barrier Basins, 
but it is of so unusual occurrence that this is hardly necessary. 
C. 6. Sand Bar Basins ( JEtangs ). Shore lagoons, shut in 
behind wave and wind-formed sand bars and dunes, are common 
along our coast from Cape Cod to Mexico; most frequently they 
are open to tide water and are consequently rather arms of the 
sea than lakes, but considered as enclosed bodies of water of 
sluggish circulation and narrow outlet, they may be included in 
our list. There are two forms to be noted : one in which the 
length of the lagoon is parallel, the other in which it is at right 
angles to the shore. The first occur south of New York and are 
formed off a gently deepening shore where the heavier waves break 
at some distance from the beach and there drop the sand they 
have lifted from the bottom; as the bar shallows it grows more 
rapidly, and finally reaches the surface, when the winds aid the 
waves and pile up the bank ten or fifteen feet above water level, 
till it makes a continuous and secure barrier. Openings are 
1 Scrope, Extinct Volcanos of Central France, 92; A. v. Lasaulx, Niederrh. Ges. 
Sitz’b., xxv, 1868, 56. 
2 Lartet, Esquisse geol. du bassin de la Mer Morte, Soc. Gdol. Bull., xxii, 1865, pi. iv. 
3 Roy. Geogr. Soc. Journ., x, 1841,458; xii, 222. 
4 Gilbert, U. S. Surveys W. of 100 Merid., hi, 111. 
