TOrOGRArHY OF LAKE SUORES. 



91 



into long, narrow, level-topped i-idges, with rounded crests, which follow 

 the broader curves but not the minor irregularities of lake shores. They are 

 composed of water-worn debris which has been assorted by currents, and 

 when exposed in cross-section tliey present an ii-regular anticlinal of depo- 

 sition. Gravel ridges of this nature have received the name of harrier-bars. 



The altitude of the horizontal crest of a barrier bar is determined by 

 the storm limit of the waves and currents that built it. Each such structure 

 therefore furnishes a record of the horizon of the water's surfiice in which 

 it was formed. Should a lake vary in level, it is evident that barrier bars 

 may be constructed at many different altitudes. In the desiccated lake 

 basins of Utah and Nevada bai-s of this nature frequently occur in con- 

 centric and synmietrically curved ridges, which may be followed for miles 

 and sometimes furnish natural highways of a most excellent character. 



An ideal plat of an arm of an ancient lake in which bai-rier bars were 

 formed at three different levels is given in tlie following figure. Below 





Fig. 10. — Ideal jilat and section iUiisti-atmg the Ibrmation of bariier bars. 



the sketch is a section through the valley on the line xi/, in which the level 

 of the surface of the lake at the time the various bars were formed is indi- 

 cated by dotted lines. 



