OEGAKIC SAND TYPE 645 



The agency of vegetation in causing granular deposits in hot springs 

 was first pointed out by Cohn in 1863, in the celebrated Carlsbad-waters.^^ 

 The granules of calcium carbonate become gradually coarser, and are 

 finally united into a compact bed of travertine. Seeley, in 1888, called 

 attention to the close resemblance between oolitic granules and the inter- 

 nodal grains of certain nuUipores, and suggested this as a possible origin 

 of some beds of oolite.*^ The studies of Weed in the Yellowstone Na- 

 tional Park led him to the same conclusion as Cohn concerning the origin 

 of the calcareous formations about the Mammoth Hot Springs.*^ Pellets 

 up to 1 millimeter in size form within the tissues of the algae and are 

 finally cemented together and their outlines lost. The same cause was also 

 found operating in the geyser regions, the plants being both algae and 

 moss, and leading to the deposition of silicious sinter (page 665). Owing 

 to the porous, incoherent, often mealy nature of these calcareous and 

 silicious deposits, they are readily disintegrated again into sand and 

 coarser fragments, giving rise to a residuo-organic subtype of sand. To 

 the extent that calcareous tufa and travertine, deposited so commonly 

 from ordinary spring water, may be found due to plant agency, these 

 deposits would belong under this same division. 



Of essentially the same nature is the oolitic sand of Great Salt Lake, 

 Utah, which was made the subject of study in 1891 by Eothpletz, of 

 Munich, who concluded that the granules originated in the tissues of 

 colonies of bluish-green algag (Gloeocapsa and Glceotliece) and are now 

 forming.** Samples of this sand were studied and described by the pres- 

 ent writer in 1899, and the conclusion reached that the Monroe oolites of 

 southeastern Michigan must have had a similar origin.*^ The Salt Lake 

 granules are well asserted, grayish white and mottled in color, about .3 to 

 .4 millimeter in diameter, the outer surfaces so smoothed and polished that 

 they resemble porcelain, and made up of concentric layers of calcium 

 carbonate, showing more or less radial arrangement. There is no nucleus 

 of quartz or other mineral present but what appears as an organic core. 

 Elongated, stick-like forms are mingled with the granules, straight or 

 slightly bent, with rounded ends and otherwise resembling the granules 

 themselves. Less frequently there occur much larger, flattened masses 



*^ Cohn : Die Algen des Karlsbader Sprudels, mit Riickslcht auf die Bildimg des 

 Sprudel Sinters ; Abliandl. der Schles. Gesell., part ii, p. 35. 



^ Seeley : On tlie origin of oolitic texture in limestone rocks. British Association for 

 the Advancement of Science, Bath meeting, 1S88, p. 674. 



*^ Weed : Formation of travertine and siliceous sinter by the vegetation of hot spx'ings. 

 Ninth Annual Report of the U. S. Geological Survey, 1889, p. 619. 



** Eothpletz : Ueber die Bildung der Oolithe. Botanisches Centralblatt, vol. li, 1892, 

 p. 267. Translation in American Geologist, vol. x, No. 5, 1892, p. 279. 



*5 Michigan Geological Survey, vol. vii, part i, 1900, p. 64, 



XLV— Bull, Geol, Soc. Am., Vol. 21, 1909 



