Davis.] 
868 
[January 18, 
usually preserved at certain points by tbe wash of tidal-currents 
and the outflow of rivers, and on a given shore line these breaches 
are prevailingly nearer one end of the bar, on account of the 
oblique average approach of waves and currents favoring the 
growth of the bar in one direction and not in the other. This is 
w~ell shown as the lagoons silt up into marshes on our Carolina 
coast by the southward deflection of rivers that feed and drain 
them; still more distinctly in the great harbors on the Prussian 
shore of the Baltic. 1 Many of these lagoons occur at the north- 
ern end of the Caspian. The salt lakes of Bessarabia, 2 on the 
northwest coast of the Black Sea, were shut in on their shallow 
shore by sand bars and dunes, and so complete a barrier was 
made that the enclosed lakes lost more by evaporation than they 
gained from leakage and their small streams, and were on the 
point of extinction, when, in 1850, an especially strong storm 
broke down the sand barrier and overflowed the old lake area 
again. By this accident, an extensive salt-industry w T as inter- 
rupted, although the lakes after the overflow were only three to 
five feet deep. 
Slight departures from the type are formed when an island is 
connected with the coast by bars at either end and a lagoon 
enclosed between the two ; examples are given by Peschel behind 
the Islands Giens, Antico and Argentario on the French, Sardin- 
ian and Tuscan shores of the Mediterranean. 3 Another varia- 
tion occurs at the head of the Adriatic where a long sand-bar 
lagoon has been divided by the growth of the Po delta. 
The second subspecies depends on the closing of a submerged 
stream- valley by a sand bar stretching across its mouth ; these 
are much rarer than the others. They are well seen on the south- 
ern shores of Martha’s Vineyard and Nantucket, where the coast 
has suffered recent subsidence. 4 The triangular et ings of the 
French Biscayan coast 5 combine the forms of the two subspecies. 
1 G. Berendt, Geol. des Kurischen Haffes . . . Erlauterung zu Sec. 2, 3, 4, der Geol. 
Karte v. Preussen. Konigsberg, 1869. A fiaished s'udy of this interesting region. 
2 G. Helmersen, Die Salzseen Bessarabiens und die Einbruch des Schwarzen Meeres 
in denselben in 1850. St. Petersbourg, Acad. Bull. Phys. Math., xvn, 369-397. 
8 Phys. Erdkunde, i, 446. 
4 W. Upham, The Formation of Cape Cod, Amer. Nat., 1879, 555. 
6 E. Reclus, Le Littoral de la France, Rev. des Deux Mondes, xxi, 1863, 682, and 
Carte de France de l’Etat majeur, sheets 170, 180, 191, 203, etc. 
