Page 144 - 1915, Springs of CA.

134 SPRINGS OF CALIFORNIA.

the ridges. The deposition of the onyx marble has apparently ceased,
and the lime carbonate that is now being deposited is in the form of
dullrbrown tufa.1
In 1893-1895 a quarry was opened in one of the ridges, and about
60 tons of the material was taken out and shipped in rough blocks
to San Francisco. It was there
cut into slabs and polished and
rfjiiiiv\\vw/f'n'&&
used in the rotunda of the City
Hall. In 1910 the deposit had
j*^1^ ^5 " / 'i-^-
not been worked since the San
Francisco order was filled, as the
nearest railroad point was 50 miles
distant. The material has a pleas-
ing mottled effect, is sufficiently
translucent to give depth to the
coloring, and takes a good polish.
At two points near these ridges
small springs, with temperatures
of 121° and 148°, rise in pools
about 3 and 10 feet in diameter.
Water from the larger pool has
3. Sketch map of travertine ridges near been used to some extent for bath-
Bridgeport, Mono County, Cal. a, Bathhouse; b, m« "m a small house near by. A
main spring; c, derrick at quarry. -,- , < i
third spring issues from a longi-
tudinal crevice in the top of one of the ridges, which is shown in
Plate IX, A. Its temperature is also 148° and its flow is perhaps
one gallon a minute. It deposits lime carbonate on troughs and
barrels that have been arranged so that the water can be used in
preparing sheep dip. This deposit is said to form at the rate of nearly
an inch a month. The water is noticeably carbonated, and the fol-

i The following notes concerning the formation of travertine are abstracted from an article by George P.
Merrill, entitled "The onyx marbles; their origin, composition and uses, both ancient and modern"
(Smithsonian Inst. Ann. Rept. for 1893, pp. 539-585, 1895).
Pure water dissolves only 1 part of calcium carbonate in 10,800 when cold, and 1 part in 8,875 when boiling;
but when saturated with carbon dioxide at 10° C. (50° F.) it will dissolve nearly 1 part in 1,000 (0.88
grams per liter). The amount is increased by increased pressure, and under the most favorable circum-
stances the amount of calcium carbonate dissolved is 3 parts in 1,000. On cooling, and especially on relief
of pressure and consequent escape of carbon dioxide, the excess of calcium carbonate is redeposited. Slow
deposition tends to produce a crystalline structure; rapid deposition tends to produce a cellular one. The
form of crystallization may also be determined by the character of the deposition, for G. Rose has shown
(Fouqu^ and Levy, Synthese des mineraux et des roches) that by humid methods it is possible to produce
out of the same solution crystals of both aragonite (orthorhombie, specific gravity 2.95) and calcite (hex-
agonal rhombohedral, specific gravity 2.72), the one or the other forming according to the temperature of
the solution. Aragonite is formed exclusively by rapid evaporation of hot solutions, while calcite may be
produced from similar solutions, both hot and cold. Most known deposits of onyx marble apparently were
formed by hot water that was probably of a high degree of saturation and under some pressure. Rapid,
cellular deposition is checked and a slower, compact, crystalline one is favored if the mineralized waters
discharge in quiet pools; hence Merrill considers this condition of formation to have been a probable one
at onyx marble deposits. Variations in the temperature of the water, the rate of cooling, and the amount
and proportions of calcium, iron, and bicarbonates in solution, and the presence of impurities, such as
clay, produce the numerous banded varieties of the stone.