ON OOLITES AND SPHERULITES 597 
beautifully illustrated paper on the odlites of the Buntsandstein of 
northern Germany,’ used as arguments in favor of an organic 
origin. The formation of the (unstable) barium sulphate sol in this 
case is possibly analogous to its formation in glycerin, as described 
by Recoura.? Barite concretions are locally found in shales.’ 
6. Calcium carbonate: In the sedimentary odlites we have all 
transitions from spherulitic to concentric structure. Perfect 
spheres of calctum carbonate, measuring 1 cm. and more in diam- 
eter, with excellent radial crystalline structure were described by the 
author from Miocene limestones of the Rhine valley.’ Calcareous 
concretions are very common. In Drew’s experiments, in which he 
proved the precipitation of calcium carbonate from sea water by 
Bacterium calcis, the first turbidity appearing in his solutions was 
caused by particles of such fine grain that they could be centrifuged 
only with difficulty. This suggests a colloid state. In the same 
experiments small spherulites were formed.’ Vaughan allowed 
bottles containing Bahaman shoal-water muds strained through 
bolting cloth of fine mesh to stand over three months, after which 
he found in them numerous odlite grains which had grown to such 
sizes as to preclude their passing through the mesh of the bolting 
cloth.° The gel of calcium carbonate resulting from the precipita- 
tion of calcium carbonate from a solution of water-soluble calcium 
salts and its tendency to form spherulites have long been known. 
Owing to the elaborate studies of Buetschli, calcium carbonate is 
perhaps the best known of the “gelatinous salts.’’” 
1 E. Kalkowsky, “Odlith und Stromatolith im norddeutschen Buntsandstein,”’ 
Monatsber. d. Deutsch. geol. Ges., LX, Part I (1908), 68-125, especially p. 122. 
2M. A. Recoura, “‘Sur le sulfate de baryum colloidal,’ Compt. Rend., CXLVI 
(1908), 1274-76. 
3 See, for instance, J. P. Rowe, ‘“‘Nodular Barite and Selenite Crystals of Mon- 
tana,” Am. Geologist, XX XIII (1904), 198-99; for a case in which the primary origin 
of these concretions is obvious see W. H. Bucher, ‘‘Beitrag zur geologischen und 
palaeontologischen Kenntnis des jiingeren Tertiairs der Rheinpfalz,”’ Geognostische 
Jahreshefte, XXVI (1913), 31. 
4 Bucher, op. cit., p. 80. 
5 G. H. Drew, ‘“‘On the Precipitation of Calcium Carbonate in the Sea by Marine 
Bacteria,”’ etc., Carnegie Publication No. 182 (Washington, 1914), pp. 30-31. 
§T. W. Vaughan, “Preliminary Remarks on the Geology of the Bahamas,” etc. 
Carnegie Publication No. 182 (Washington, 1914), pp. 51-53. 
7Q. Buetschli, Abh. Goettinger Akad., N.S., IV, 1908. 
