438 BOTANICAL GAZETTE [JUNE 
fig. 1 shows a pond in the edge of the village, adjoining a 
road. On July 2 there was a thunder shower lasting for about 
an hour. During that time a deposit was formed at one corner 
of this pond some 25%+'™ in area and 30-90™ in depth. Four 
weeks later came another, less violent shower. The surface of 
the first deposit was cut down part way across by 40-50™, and 
Fic. 1.—Pond in edge of village. 
the material, aggregating many tons, borne farther out. The 
obliteration of this pond within two or three years may be 
expected. Of course, we are here dealing with highly disturbed 
conditions, but nevertheless the case may serve to enlarge our 
ideas as to the rapidity with which silt may be moved down. 
During the early period immediately following the retreat of the 
glacier, and before vegetation gained a footing, deposits in these 
_ depressions must have been made with enormous rapidity. — 
| Where the pond is surrounded by grassy fields, the washing: 
_in process is much restricted. That it still goes forward, how- 
_€ver, one need only examine the pond margin to learn. 
A zone — 
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