THE TOl'OGKArHV OF LAK1-: SHOUES. 



49 



a delta, is made to the land. The most instructive deposits of this nature 

 occur where high grade streams enter a lake, as when a lake washes the 

 l)ase of a mountain range. In such an instance, pebbles and water-worn 

 Ixudders are swept along by the stream until it mingles with the quiet 

 lake water, where its velocity is checked and the coarser portion of its 



Fig. (J —Map of sand bars: South shore of Lake Oxtario. 



load dropped; fine sand is carried beyond and deposited about the outer 

 margin of the accumulation of boulders and pebbles, and the finer 

 material held in sus})ension is transported still fartlier from shore and dis- 

 triljuted over the lake l)()ttom. The coarse material is deposited alxiiit 

 the mouth of the stream in a semi-circular pile, the base of which is 

 beneath the water and the apex some distance above, Avhere the stream 

 begins tolose velocity. The pile is built out in all directions in which llic 

 water has freedom to How, and a semi-ciivular or occasionalh- a tnil\- 

 delta-shaped addition is made to the land. 



Fine examples of deltas, built by swift streams adjacent to a precipi- 

 tous shore, occur on the west side of Seneca lake. New York, near Wat- 

 kins. In these deltas the action of sliore currents from Ixtth the north 

 and south is conspicuous, and the deposits liave l)eeii cut away so as to 

 leave a triangular or markedly delta-sliaped outline, but the ai)ex of each 

 delta points lakewaid. instead of towaid tlii' shore as is the iionnal 



