. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. CARBONATES 105 a loose friable deposit made by springs and streams either by evaporation or through intervention of algous vegetation. Such are often beautifully arborescent and of a white color, as seen at the Mammoth Hot Springs of the Yellowstone National Park. Somewhat similar deposits are formed by springs in Virginia, California, Mexico, New Zealand. Tufa deposits of peculiar imitative shapes have been described by Mr. I. C. Russell of the United States Geological Survey, as formed by the evaporation of the waters of Py
. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. CARBONATES 105 a loose friable deposit made by springs and streams either by evaporation or through intervention of algous vegetation. Such are often beautifully arborescent and of a white color, as seen at the Mammoth Hot Springs of the Yellowstone National Park. Somewhat similar deposits are formed by springs in Virginia, California, Mexico, New Zealand. Tufa deposits of peculiar imitative shapes have been described by Mr. I. C. Russell of the United States Geological Survey, as formed by the evaporation of the waters of Pyramid Lake, Nevada. Oolitic and piso- litic limestones are so called on account of their rounded, fish-egg-like structure, the word oolite being from the Greek work oiov, an egg. (See PL 11.) These are in part chemical and in part mechanical deposits. The water in the lakes and seas in which they were formed became so satur- ated that the lime was deposited in concentric coatings about the grains of calcareous sand on the bottom, and finally the little granules thus formed became cemented into firm rock by the further deposition of lime in the interstices. This structure will be best understood by reference to Fig. 7. Eoeks of this nature are now forming along the beaches of Pyramid Lake. Such forms as these may or may not show a nucleus. It seems safe to assume that such a nucleus, at first, in all cases existed, though it may be in microscopic dimensions only. Travertine is a compact and usually crystalline deposit formed, like the tufas, by waters of springs and streams. The traver- tines are often beautifully veined and colored by metallic oxides and form some of the finest marbles. Such are the so-called ''onyx marbles" of Mexico and Arizona.^ =^Tlie Onyx Marbles, Ann. Eep. U. S. National Museum for 1893. Also Stones for Building and Decoration, Wiley & Sons, ISTew York, 2d ed., p. Pig. 7.—Microstructure of oolitic Please note that these images
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