TOPOGEAPHY OF LAKE SEORES. 93 



although the adjacent beacli may be composed of gravel and boulders. 

 They are not shore ridges submerged by a rise of the lake, for the reason 

 that they are in harmony with existing conditions, and are not being 

 ei'oded or becoming covered with lacustral sediments. 



In bars of this character the fine debris arising from the comminution 

 of shore drift appears to be accumulated in ridges along the line where 

 the undertow loses its force ; the distance of these lines from the land 

 being determined by the force of the storms that carried the waters shore- 

 ward. This is only a suggested explanation, however, as the complete 

 history of these structnres has not been determined. 



EMBAXKMEKTS. 



The combined action of waves and currents along shores of moderate 

 slope results, as we have seen, in the formation of cut terraces, sea-cliffs, 

 built terraces, and barrier bars. When the shore becomes steep or any 

 abrupt change in its direction takes place, as when the mouth of a bay is 

 reached or a promontory projects from the shore, the current does not 

 follow the sinuosities of the land but continues its course, and, on entering 

 deeper water, loses its power of transportation and deposits its load. 

 Fresh material is carried along in a more or less continuous stream by 

 the shore current and added to that previously deposited, thus forming 

 a subaqueous embankment. This process is continued until the deposit is 

 raised to the level of the barrier bar or terrace, as the case may be, along 

 which the current-borne debris is carried. This process continuing, the 

 embankment increases in length but not in height; its crest, like that of a 

 barrier bar, has its height determined by the horizon of the lake surface. 

 It is evident from their mode of formation that embankments are but jiro- 

 longations of built terraces and barrier bars; in fact one form merges into 

 the other in such a manner that it is not always possible to determine in 

 which list a given structure should be placed. 



The formation of embankments will, perhaps, be rendered more intelli- 

 gible by referring to the accompanying topographic sketch, in which a por- 



