








METER Nad eA yee 9 0 Ain See, ae ah ape Pe A s : 
“aes ent RN Tee eel Te i i me eS gh ae ie 
ch eee eee 4 es eee yan te f ; ae ’ ~ x 
ked, and its sediment begins to spread in fan-shape over the 
bottom (¢ in Fig. 122). Every 
butary stream brings in its con- 
tribution of detritus. In this way a 
series of shoals is pushed out into the 
e (Fig. 123). This phenomenon 
may frequently be instructively ob- 
served from a height overlooking a Fie. 122.—Srreamier (6) ENTERING A 
small lake among mountains. Atthe = SMart He (a), AND DEPOSITING 
mouth of each torrent or brook lies a Este Sie ade 

Fig. 123.—Pian or A LAKE ENTERED BY = Fie. 124.—Laxe (a8 IN Fic. 123) FILLED UP 
‘THREE STREAMS (c, d, €), EACH OF AND CONVERTED INTO AN ALLUVIAL 













_ (a,b) at rvs Moura. 
es \ 
united lakes of Thun and Brienz at Interlaken. Or by the advance 
of the alluvial deposits the lake may be finally filled up altogether, 
as has happened in innumerable cases in all mountainous countries 
(Fig. 124). The rapidity of the infilling is sometimes not a little 
remarkable. Since the year 1714 the Kander is said to have thrown 
into the Lake of Thun a delta measuring 230 acres, now partly 
; woodland, partly meadow and marsh. 
In the case of a large lake whose length is great in proportion 
to the volume of the tributary river, the whole of the detritus may 
pe deposited, so that, at the outflow, the river becomes as clear as 
‘when its infant waters began their course from the springs, snows, 
and mists of the far mountains. Thus the Rhone enters the Lake 
_ of Geneva turbid and impetuous, but escapes at Geneva as blue 
_ translucent water. Its sediment is laid down on the floor of the 
lake, and chiefly at the upper end, as an important delta which quite 
Tivals that of a great river in the sea. Hence, lakes act as filters or 
‘sieves to intercept the sediment which is travelling in the rivers 
from the high grounds to the sea (pp. 373, 392). eet 
_ (e) Bars and Lagoon-Barriers.—If we take a broad view of 
terrestrial degradation we must admit that the deposit of any 
3 | scare 
(a) In Lakes.—When a river enters a lake its current is at once — 
p I. Sxor. ii. §3.] RIVER DEPOSITS. See 
- 
‘WHICH DEPOSITS A CONE OF SEDIMENT PLAIN BY THE THREE STREAMS, ¢, d, 6. _ 
