i88i.] 
Miniature Physical Geography . 
637 
This continued until the isthmus of land was eaten through, 
whereupon there was at once a flow of water through this 
opening, which was in consequence soon broadened and 
deepened to such an extent as to admit of the passage of the 
whole river through this channel. The loop was thus left as 
a horse-shoe lake in connection with the river. 
Those who have passed down the Mississippi from 
St. Louis to New Orleans will doubtless be able to recolleCt 
passing through more than one “ cut-off” of this nature, and 
thus shortening the journey by perhaps eight or ten miles. 
An instance of the same thing, which took place on the 
Jurua, a Brazilian river, is described by Brown and Lidstone 
in the following sentence ; — -“Within the last six years the 
river has altered its course, by cutting through a neck of 
land, thereby taking a short cut and abandoning a long 
curve.” The upper end of this curve was subsequently 
silted up. 
I remember well, as a boy, anxiously watching the nar- 
rowing of the isthmus separating the two concave banks of 
such a loop on the Wey, a tributary of the Thames. And I 
have a vivid recollection of the occasion of my first 
“ shooting” in my canoe the rapid which was formed when 
the bank had at last given way. 
V. The Formation of Islands. 
To revert now to the miniature river: in the midst of the 
stream sand-islands are from time to time formed, often 
caused by a stranded stick, and partly no doubt by the deep- 
ening of the main channel on one side or the other ; but no 
sooner has the sand of which they are composed become dry 
than the treacherous stream commences the destruction of 
that which it has itself produced. This it generally begins 
at the upper end, and it is not uncommon to see construction 
and destruction going on at the same time ; destruction 
above, construction below. Where this double action takes 
place the island is not stationary, but in motion down 
stream. 
Whether this motion down stream has been observed on a 
large scale I do not know ; but that the construction and 
destruction of islands take place with considerable rapidity 
in some of the larger river channels there can be no doubt. 
In one of my note-books I find the following remarks, written 
on board a Mississippi steamboat : — “You can see islands in 
all stages of formation in the river. First, an extensive shal- 
low or shoal ; against the upper portion of this logs and 
