154 
following manner. The green plants re- 
quire carbon di-oxide for the processes of 
assimilation and they take it from the 
water, which means, in this case, the depo- 
sition of a certain amount of calcium car- 
bonate. There are many plants that have 
the power of taking calcium carbonate 
from water. Chara, the stone-wort, the 
marine alge called Corallines, forms of 
the group Siphonez inhabiting the coral 
sands of Burmuda and Florida, are exam- 
ples, and besides these there are species of 
Cyanophyceee closely related to the forms 
actually found in these hot springs. If the 
tufts and felts be teased out, one may find 
innumerable crystals of calcium carbonate, 
varying in size, held in the meshes of the 
filaments. We have tried to show the ap- 
pearance of such a preparation in Fig. 6. 
One may observe this very significant fact 
that the crystals at the bottoms of the tufts 
and sheets of alge are large, and there are 
places where they have become cemented 
together into flakes of mineral deposits. In 
the middle region and towards the surface 
of the felts the crystals are small and scat- 
tered. It is evident that these expanses of 
algal growth lay down sheets of calcium 
carbonate and that the tufts build up little 
mounds upon the generally smooth sur- 
face. 
Tt is altogether probable that the mineral 
deposits follow the development of the 
algee very closely and actually entomb the 
older filaments at the bottom of the 
growths in limestone crypts. It is inter- 
esting to know that the first travertine 
thrown down in these waters is probably 
associated with the vegetation at the time 
of the deposit. We say probably because 
the fact cannot be proved in these hot 
springs, but we can reason from analogy, 
for the conditions here are quite similar 
to those of the waters of Carlsbad, in Ger- 
many. There the springs issue from 
granite rocks and the travertine is not de- 
SCIENCE. 
(N.S. Von. VI. No. 135. 
posited until traces of vegetation appear in 
the water. ‘These interesting observations 
were made by Ferdinand Cohn. As all 
the streams of Mammoth Hot Springs issue 
from travertine deposits, it is impossible to 
tell exactly where the deposition first 
begins. 
However important these alge may be 
in their rdle as rock-formers, a greater in- 
terest attaches to them because most of 
the beautiful seulpturing and coloring of 
Mammoth Hot Springs is directly due to 
their presence. The rims on the pulpit 
basins (see Fig. 7) are covered with a 
growth of algze. The interiors of the basins 
are lined with sheets of green and yellow 
on a white background, but it is the out- 
side of the basins that exhibits the most 
beauty. There are pillars and flutings and 
stalactite-like structures all colored brown 
and orange and green. ‘The alge are re- 
sponsible for almost all these peculiarities. 
If they were not present the water would 
flow in shallow sheets and fresh deposits 
of calcium carbonate would be laid down 
like so many coats of whitewash with un- 
- relieved monotony. 
But the algz change the conditions. 
Here they grow in ropey welts down the 
sides of the pulpits from the lips of the 
basins; there they have formed a raised rim 
upon some flat surface and partially dam 
up some small pool or stream of water. 
Here they hang down from some projecting 
ridge as a slight fringe that drips water. 
Everywhere the growth of vegetation is 
but a thin veneer over a skeleton of mineral 
deposits that follows closely the lines of 
the algal sheet. The filaments project 
from a granular and gritty deposit envelop- 
ing the fibers that are not so fortunate as 
to be at the immediate surface. Conse- 
quently when, for some reason, the water 
ceases to flow over a certain part of the 
formation, and the colored vegetation dries 
up and entirely fades out in the fierce glare 
