1889. | NEW YORK ACADEMY OF SCIENCES. 1%3 
of it remains suspended for many days, orindefinitely. Settling- 
reservoirs will not do much to purify water at such times, the 
times of all others when purification is most needed ; and there 
is nothing that will do so except filtration. The question of the 
Quaker Bridge dam rests so largely upon matters of engineering, 
that it will probably be decided, ultimately, more upon such 
grounds than upon any other; but it is well that we should 
know exactly what can and what cannot be expected of it in the 
matter of improving the quality of Croton water. 
Mr. ORLANDO B. PoTTER made remarks upon some of the 
difficulties and objections connected with the proposed great 
reservoir, and favored rather the construction of a number of 
smaller basins, by building dams in the valleys of tributary 
streams. He referred also to the ultimate inadequacy of the 
Croton water-shed for the needs of the future metropolis, and 
suggested, in that event, an extension of the Westchester aque- 
duct system into Connecticut, so as to reach and utilize the 
streams flowing into the Housatonic. 
Dr. A. A. JULIEN spoke of the organic growths that tend to 
contaminate reservoirs and ponds, and pointed out their usual 
occurrence in shallow waters and near the surface. A large 
deep body of water, such as the proposed Quaker Bridge reser- 
voir, would in this respect have much advantage relatively over 
smaller and shallower ones. 
Dr. NEWBERRY remarked that there was much to be said on 
both sides of the question of the Quaker Bridge dam. It was 
undoubtedly true that the water supplied to the city would be 
purest if it could be stored in deep rock-walled reservoirs like 
some of our lakes, Mahopac, Mohonk, and others. In such 
deep reservoirs the water would be kept relatively cool, would 
be clarified by the settling of suspended impurities washed in 
in time of flood, and if the outlet were near the surface such 
impurities would be left undisturbed. Again, the animal and 
vegetable organisms which in their decay contaminate drainage 
waters are confined for the most part to shallows where the 
depth of the water is fifteen feet and less, and where it is warmed 
by the sun’s rays. The Quaker Bridge dam would have more 
