The geological work of Mosses and Algoe. — Weed. 53 
remains of the same species of diatoms that now form the thick 
ooze of the warm marshes.* 
The separation and secretion of silica from natural waters is, 
however, not confined to the diatoms. The alkaline waters of the 
geysers and hot springs of the Yellowstone park which are highly 
charged with silica, contain a vividly colored algous vegetation 
that produces siliceous sinter, and mosses growing in the cooled 
waters of certain of the springs produce rock-strata also formed 
of silica. 
The separation of the silica b}' algaj is a very common phenom- 
enon in the Yellowstone park and inferential!}' in hot siliceous 
waters elsewhere since the same algse species occur in the hot 
waters of New Zealand, the Azores and other localities. The 
alga? extract the silica and deposit it as a hydrated jell}*, that is 
sometimes an integral part of the plant tissue, and forms the 
hyaline wall of the algse threads, sometimes encrusts the silken 
filaments or more often forms a thick jelly that binds together the 
matted felt of threads into slimy cushions or into leathery sheets 
that line the cooler springs of 90 degress to 130 degrees F. , or 
occurs as a slippery coating upon a hard deposit of sinter. The 
evidence! is convincing and conclusive that these growths form 
masses of jelly that harden into and form siliceous sinter. 
Equally strange is the formation of terraces of a bufF-colored 
rock consisting of 90 per cent, silica, by the moss Hypnum adun- 
cum var. gracilescens. This moss covers the inner and outer sides 
of a series of terraced bowls at the upper geyser basin of the Yel- 
lowstone park, and it was easy to show that the moss passed di- 
rectly and in situ into the stone beneath. Indeed the rock itself 
shows at once that it is composed of the silicified (?) or siliceous 
stalks, of this moss. Specimens in the possession of the survey 
show that the silicification of the older portion of the moss stalk 
takes place even while the stems wave loosely and freely about in 
the water. The analysis of the siliceous rock thus formed shows a 
very low percentage of organic matter considering its origin, with 
a larger amount of CaSO s , than either the siliceous sinter formed 
by alga\ or the true ge}-serites of the geyser basins. 
*Diatom beds and diatom marshes of the Yellowstone National Park, 
by Walter Harvey Weed. Botanical Gazette, Vol. \iv, No. 5, p. 117. 
(Ninth Ann. Report Director r. s. <;. s. Formation of Hut Spg. De- 
posits. Walter Harvey Weed. p. 655. 
