280 
live, grow, and multiply they remove 
carbon dioxide from the water during 
photosynthesis. As the lime dissolved 
in the water is in the form of the un- 
stable bicarbonate, H,;Ca(CO,)>, the 
removal from the water of carbon di- 
oxide, which helps to keep the bicar- 
bonate in solution, causes the rever- 
sion of the bicarbonate to the insoluble 
carbonate, which is precipitated, and 
water. H,Ca(CO,;),.—2CO,=CaCO, 
+H,O. This process is the same for 
both cold and hot waters, with the 
exception that perhaps evaporation 
and release of pressure may play a 
larger part in freeing hot waters of 
carbon dioxide. As the solubility of 
carbon dioxide in water decreases with 
increase of temperature, it would seem 
that the warming of lake waters in 
summer, the optimum season of algal 
activity, would assist the algae in pre- 
cipitating lime. The visitor at Mam- 
moth Hot Springs in Yellowstone Na- 
tional Park, where lime is deposited as 
travertine, and in the Geyser Basin, 
where siliceous sinter or geyserite is 
deposited, will note the colors dis- 
played and will understand that many 
of these are principally caused by dif- 
ferent species of algae (Weed, 1889). 
Both here and at the hot springs at 
Thermopolis, Wyo., and elsewhere, 
filaments of algae can be seen in the 
hot waters. That these algae may not 
have as much to do with the precipita- 
tion of lime as Weed assumed seems 
to be proved from the observations and 
experiments of Allen (1934). The rate 
of deposition of travertine from hot 
springs is rapid, but variable, some- 
times averaging 20 cm. per year. Howe 
(1932, p. 61), describing “‘water bis- 
cuits,’ quotes Pollock as estimating 
that blue-green algae may deposit marl 
at the rate of one foot in 75 years. 
How long it took to precipitate 20 cm. 
on a Whisky Basin pillar is indetermi- 
nate, but must probably be reckoned 
in decades, perhaps hundreds of years. 
As the lime-precipitating algae, like 
all chlorophyll-bearing plants, require 
sunlight, it follows that the waters in 
which the pillars of Whisky Basin de- 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
veloped were shallow and seasonally, 
at least, relatively clear. It is con- 
sidered that fresh-water algae cannot 
function well in depths of more than 
10 m. (Cloud, 1942, p. 371). This 
accords with the aspect of the sedi- 
ments of the Green River and Bridger 
formations, which were deposited on 
flood plains that included sloughs, 
marshes, ponds, and lakes. These 
waters were the habitat of many kinds 
of fishes, turtles, and crocodiles. The 
swamps and adjacent plains supported 
ferns, palms, laurels, elms, beans, and 
many other plants indicative of a warm 
temperate climate; and the land ani- 
mals included birds, rodents, insectiv- 
ores, carnivores, and large herbivo- 
rous odd-toed titanotheres. As time 
passed, the meandering streams of 
the Bridger plains doubtless on occa- 
sion shifted their channels or changed 
courses, making new ponds and 
marshes and filling old ones with 
sediments. Trees or shrubs inun- 
dated by these processes would in time 
be killed and become snags along 
the shore. 
Such, then, are the basic facts that 
can be read from the Whisky Basin 
pillars themselves and their geologic 
setting. Can these facts now be ar- 
ranged in orderly sequence to explain 
satisfactorily how the pillars originated? 
The clue to the solution of this prob- 
lem and beginning of its unraveling 
patently lies in the irregular boundary 
between the inner and outer zones of 
the specimens—the surface on which 
the algae first settled and deposited 
the first lime. What was that surface? 
It had to be a surface on something 
substantial, relatively slender, and up- 
right, for it is obvious that such algae 
could not start on nothing and build 
up a long, thick, relatively uniform 
cylinder of lime. Further, this sup- 
port, after serving as scaffolding for the 
algae, had to disappear in whole or in 
part so that silica could fill the space it 
vacated and form what is now the 
inner zone of the structure. The only 
substance that fulfills these require- 
ments, under all the conditions stated, 
