402 
its outlet may become obstructed. The result is the formation of a pond. 
If a young sinkhole is obstructed, a small and relatively deep pond re- 
sults. The obstruction of an old sinkhole results in the formation of a 
shallow pond of considerable area. 
Destruction—The ponds are no sooner formed than their destruction 
begins by means of those factors which destroy all such topographic forms. 
Few of them overflow, anl these only for a short time. Plant deposition 
and the deposition of silt are the two principal factors operating for their 
destruction. A pond formed in a young sinkhole which is located at or 
near the summit of a hill, i. e., near the level of an old peneplain, does 
not have as much silt washed into it as does a pond formed in an older sink- 
hole or one that is located on the lower slope of a hill. Plants are rela- 
tively a much greater factor in the destruction of the former than in the 
latter. 
Our pond belongs to the first class. It has some clay deposited in it. 
but plant debris forms the major part of its sediment. The rate of its de- 
struction is known approximately for a period of 24 years. In 1887, it was 
about eight or nine feet in depth (“deep enough to swim a horse’’). It is 
now Slightly less than four feet, a difference of four feet, or one-fifth foot 
deposition per year. So far as I know, this is the only case where the rate 
of plant deposition is reducible to even approximate figures. 
The water is usually clear. A scum of iron oxide was found on the 
surface April 1, 1910. On August 12, 1910, the water had a dark purplish 
tinge, due to the decay of organic matter. The only time the pond was seen 
to be muddy was after the rain of July 14. On this date it was quite 
opaque and of a yellowish tinge, from the suspended silt. Silt is carried 
into the pond only after very heavy rains, for reasons previously stated. 
METHODS. 
For collecting insects, insect larvae, algze, amphibian larvee, etc., ordi- 
hary insect nets and dip nets made of bobbinet and scrim, were used. A 
very useful net for collecting micro-organisms, when quantitative work is 
not demanded, is a sampling net, manufactured by the Simplex Net Com- 
pany, Ithaca, New York. It is made of bolting cloth No. 20, is three inches 
in diameter, twelve inches long, and is operated by being thrown out into 
the water and then drawn in. The ring is quite heavy so that it will sink 
