Toi'0(;j;.\i'iiv OF lakk siioiiks, 05 



the finer particles carried aloiifj by tlie current arul lield in HiiKpenHion for 

 some time after tlie coarser material lias been deposited ; as tlie structure is 

 prolong'ed this fine df'hrii beconries buried beneath the gravel arifl stones 

 conriposinjr the major part of the embankment, and many times becomes 

 folded and crumpled owin;^ to the weij^ht of the superimposed mass. 



The action of waves and currents in fornnw^ embankments is subject 

 to a multitude of variations dependent on the topoj^raphy of the shores, on 

 the character of the material moved, on changes in the <lirection of winds 

 and currents, and on many other conditions. Ah may ])(; imagined, the 

 resultant forms are er^ually diverse. Should a lake be also subject to great 

 fluctuations of level, the structure and grouping of the embankments will be 

 still more complicated. A\'hen a lake rises, new embankments and built- 

 terraces are formed above older ones ; when it falls, previously formed 

 structures are cut away and remodeled into new forms. In the first instance, 

 a line of division or an unf;<'n)formabilitv will mark the junction of the older 

 and the newer deposits ; such an example is shown in cross section at a in tlie 

 following figure, which represents contiguous built-terratjes of different date: 

 the altered conditions njay also he recorded b}' changes in the character of 

 the material of which the embankments are formed. In the second instance, 



Tifi. 12.— I>iajptiuM iUuotratiojf tii« rtUtJr* age of grav*! ttimoM MiA e«il/wikfo«nt«. 



i e., when the lower stnacture is formed subsequently to the upper, the un- 

 conffjrmity is of a different nature as is illustrated by section h; m an 

 instance of this nature the scarp of the older structure is quite commonly 

 somewhat modified by erosion. When current-built embankments of dif- 

 ferent dates are not contiguous, as represented at c, their relative age cannot 

 be determined in the same manner as in the previous examples. 



Sometimes a current in sweeping past a promont^^ry will build enjbank- 

 ments tangent to it, which become cun-ed or sickle-sliapc^l at their free ex- 

 tremities, as is illustrated on Plate XIX ; again, such embankments may 

 curve abruptly at the end so as to resemble the letter J, and are conven- 



