
“parr Il. Srcr. ii. §3.] RIVER DEPOSITS. 387 
Conspicuous examples of the formation of detrital bars may 
occasionally be observed at the mouths of narrow estuaries, as at e in 
Fig. 125. A constant struggle takes place in such situations between 
the tidal currents and waves which tend to heap up the bar and 
block the entrance to the estuary, and the scour of the river and ebb- 
tide which endeavours to keep the passage open. | 
Another remarkable illustration of the contest between alluvium- 
carrying streams and the land-eroding ocean is shown by the vast 
lines of bar or bank which stretch along the coasts both of the 
Old and the New World. The streams do not flow straight into 

- Fig. 126—Pian or Coast Bars anp Lagoons. Coast or Fiorqa. 
the sea, but run sometimes for many miles parallel to the shore-line, 
accumulating behind the barriers into broad and long lagoons, but 
eventually breaking through the barriers of alluvium and enterin 
the sea. Ona small scale examples occur on the coasts of the British 
Islands as at Start Bay, Devon (Fig. 127), where the slates (e) with 
their weathered surface (d) are flanked by a fresh water-lake (ce), 
ponded back by a bar (6) from the sea (a). The lagoons of the 



a a> * ote 
a AAR Cee 5 ~S 
. . 
SE ST ae G . 
_— fe eon. Yorn — 
ee ae x wT. ~ 
Fig. 127.—Sxcrion Bar anp Lagoon, Suapton Poot, Start Bay, Devon (B.). 
Ttalian coast and the Kurische and Frische Haf in the Baltic, near 
Dantzic, are familiar examples. A conspicuous series of these 
alluvial bars fronts the American mainland for many hundred miles 
round the Gulf of Mexico and the shores of Florida, Georgia, and 
North Carolina (Fig. 126). A space of several hundred miles on 
the east coast of India is similarly bordered. HE. de Beaumont, 
indeed, estimated that about a third of the whole of the coast-lines 
of the continents is fringed with such alluvial bars.’ 
On a coast-line such as that of Western Europe, subject both to 
‘powerful tidal action and to strong gales of wind, many interesting 
illustrations may be studied of the struggle between the rivers and 
the sea, as to the disposal of the sediment borne from the land. De 
1 Lecons de Géologie pratique, i. p. 249. In this volume some interesting examples 
of this kind of deposit are described, 
2 Oo 2 
