1889. ] NEW YORK ACADEMY OF SCIENCES. 119 
bottom will be in contact with stagnant layers; and here will be 
the precise conditions for creating new contamination. 
An incident came under my observation several years ago 
which serves to show the effect, upon pond-waters, of organic de- 
composition. It was an ancient pond covering more than a 
score of acres. The bed, to the depth of about five feet, was of 
soft black mould and fibrous material, upon a gravelly bottom. 
The pond was drained to make way for improvements. Several 
families had lived close to it; three generations were sallow and 
saturated with malaria and fever. The withdrawal of the water 
from the pond caused their wells to run dry, which compelled 
a lowering of the wells. Thus water was obtained from another 
and purer source. After the pond was drained and the wells 
deepened, the people of this humble community were healthier 
than for thirty years. Here we see that filtration of contami- 
nated pond-water through gravelly soil does not effect its puri- 
fication. 
Some time ago, while walking through the Park, I observed 
workmen gathering deposits from the bed of the westerly com- 
partment of the old reservoir. It was a dark, soft substance, of 
offensive odor, and was being carted away to be used as a fertil- 
izer. Deposits of this sort, when allowed to accumulate upon 
the bed of any pond for a series of years, would become a source 
of abominable contamination. 
There is no question but that New York could build a wall 
high enough and strong enough toimpound all the waters of the 
Croton, and if necessary Jine the bed with metal to prevent escape 
of water through fissures. But further than this, the stone and 
cement engineers who calculate the amount of the masonry and 
the number of gallons it will impound, are no longer helpful. 
They have certified that only by means of this great dam will it 
be possible to serve the Croton to New York City. Yet to the 
philosophical engineer it is well known that by auother method 
the supply can be made equally ample, and without creating 
conditions of contamination. 
DISCUSSION. 
Mr. FRANCIS COLLINGWOOD remarked:— 
Mr. PRESIDENT:—I have had no opportunity to make any 
preparation for discussing the paper we have just heard, but 
cannot allow it to pass unchallenged. 
The writer has attacked the project for a dam at Quaker Bridge, 
on the ground that the reservoir thus formed will have insuffi- 
