Davis.] 
348 
[January 18, 
C. 1. Fan-Delta Barrier Basins} It sometimes happens that 
a lateral stream carries more detritus into a valley than the main 
stream can carry away ; the surplus then accumulates as a fan- 
shaped delta, highest where it enters the main valley, spreading 
and sloping radially across it, and driving the main stream as far 
as possible to the opposite side. 2 So much is frequently accom- 
plished ; but as this change narrows the main channel and quickens 
its current, the transporting power is thus increased, and the pas- 
sage is ordinarily cut low enough to prevent the formation of 
lake. The Rhone, just above St. Maurice, between Lake Geneva 
and Martigny, has thus been crowded close to the eastern side of 
its valley by a heavy delta of gravel and rock brought down a 
ravine from the Dent du Midi, and *to which great additions were 
made in 1835, but no lake was formed. 
Pangkong in the Himalaya, back of Kashmir, is a good example 
of a completed lake of this species : it is a long, narrow stretch 
of water between steeii mountain banks, and near the point where 
as a river it would flow into the Shyok, a lateral stream has 
formed a great delta-deposit and held it back. So effectually is 
the barrier made that no outlet flows across it: whatever escape 
the lake has must be through the gravel underground, but that 
much of the supply is counterbalanced by evaporation is shown 
by the brackish taste of the water. At other points in the same 
valley, lateral deltas nearly succeed in breaking the continuity of 
of the lake. 3 Some of the high lakes of Western Tibet, between 
the Karakoram and the Kuen Lun, seem to be of similar origin 
but the amount of detritus deposited about them is so great as to 
make the early relations of drainage doubtful. 4 
The separation of Lake Brienz from Lake Thun is accomplished 
by the combined deltas of the Lutschine and Lombach, entering 
1 Peschel names this species Sonldar' sche Seen , after the discoverer, as he supposes, 
of their origin. Phys. Erdk., ii, 328. But they were understood earlier, as the notes 
below show. 
2 Excellent figures of such deltas are given by Drew. Geol. Soc. Journ., xxix, 
1873, 441 — . 
3 Dre w, Jummoo and Kashmir, 323. Tso-Moriri is of similar origin, p. 302. 
4 Id., 331. 
