54 The Aim rial ii Geologist. Jan. isoi 
SiO a 89.72 
A1 2 0., 1.0-- 
CaO 2.01 
II. ,0 7.34 
Total 100.09 percent 
Both the deposits of silica formed by mosses and those result- 
ing from algous life are notably pure, containing less clay than is 
usual in the true geyserite formed by evaporation. 
It has long been known that certain algae, called Beggiatoa, 
are the characteristic inhabitants of sulphur springs, and the 
white slimy masses which the}- form were at first considered to be 
a lifeless organic substance precipitated out of the warm waters. 
In studjing these alga? it was noticed that they were often assoc- 
iated with deposits of sulphate of lime and that the minute 
threads were encrusted by sulphur. Cramer and other observers 
proved that the filaments contained granules of amorphous sul- 
phur. In common with other students he supposed this sulphur 
to be derived from the deposits of sulphate of lime and from the 
soluble sulphates present in the spring waters. Quite recently, 
however, it has been shown by the painstaking and convincing 
experiments of Winogradsky, that these plants actually form de- 
posits of CaSOj in the following manner. Unlike other alga?, the 
Beggiatoa subsist upon and are nourished b}- H.S which the sul- 
phur waters contain in greater or less quantity. This they de- 
compose into water and sulphur, the latter being secreted within 
the alga? threads in amorphous white granules. These immedi- 
ately crystallize upon the death of the plant, but during its life 
are oxydized to H,SO r which is immediately neutralized by the 
carbonates present in the water and forms sulphates, and if 
CaS0 4 be present in large quantity it is deposited as gypsum. 
If the results outlined above are attained in this way (and there 
seems no reason to doubt the careful experiments mentioned), the 
Beggiatoa stand alone in the vegetable world. That the sulphur 
is necessary to the growth of the plant was proven by the impov- 
erishment of the plant as the sulphur was consumed and its death 
when the supply was exhausted. 
It is believed by the French biologist Parize* that microbes 
*Trouessart — Microbes, Ferments and .Moulds. Inter. Sci. Series. No. 
56, p. 124. 
