320 THE AMERICAN MONTHLY [Oct. 



gets that the silica in the loricfB of bacillaria, or diatoms, 

 is in a very soluble form and bacillaria are also present 

 in all water, marine, brackish and fresh, tiie world over. 

 Silica can also be dissolved when in the crystaline form, 

 as clear, transparent rock crystal. It is very li-kely that in 

 this manner silica comes into solution and not by the ac- 

 tion of alkali, potash or soda, which are also common in 

 all soils. But, he says, "such being the case there must 

 be a great abundance of dissolved silica in the Brooklyn 

 water, and something in the nature of the water-shed 

 which enables it to impart the silica. As a matter of 

 fact, the ponds and streams contributing to the Brooklyn 

 supply have sides and bottoms of sand, which is silica in 

 an undissolved form." But silica is always soluble! 

 "Moreover all the water has an alkaline reaction and is 

 capable, therefore, of dissolving silica and holding it in 

 a soluble form. The wells, indeed, are the chief source of 

 the silex of the Brooklyn water. The complete analysis 

 of the mineral constituents given later shows the wells to 

 contain 1.5 parts per 100,000 of silica. But by dilution with 

 the surface waters containing relatively less, the silica in 

 the combined supply is only about half as much. But 

 even then, it amounts to 9 per cent of the total mineral 

 matter present. This large amount is more than ample 

 for the nutriment of the enormous number of silicious 

 algSB which thrive and multiply in the Brooklyn resevoirs 

 and distributing mains. 



Where do these Bacillaria come from? A microscop- 

 ical examination of the water from several Brooklyn shal- 

 low wells, shows a few Bacillaria, the Asterionella, how- 

 ever, beiug found but once. From one basin however 

 they were plentiful, being 6,400 per cubic centimetre. 

 The sample taken from the centre, but at the bottom of 

 the resevoir, at the same time, contained 11,616 and the 

 efflux 9,552 Asterionella. 



Besides the silica, what else in the way of food do the 



