ON OOLITES AND SPHERULITES 595 
radial and concentric structure depends on the amount of other 
substance thrown out simultaneously with, and mechanically en- 
meshed in, the growing structure. 
Ordinary concretions seem to differ only in size and, in many 
cases, in an excess of mechanically enmeshed materials. That 
these principles underlie the formation of most, if not all, sedimen- 
tary odlites, spherulites, and concretions is rendered probable by 
the fact that almost all substances which are known in one of these 
forms are also known in the others and are the same that are known 
to occur extensively in nature in the colloidal state. A brief review 
will emphasize this relation. 
Review of natural odlites.—1. Silica: Des Cloizeaux found 
spherulites of clear silica in a jelly-like paste.* Spherulitic hyalite 
was observed by Jimbo from the Etchu province of Japan, and 
similar hyalites with concentric structure from hot springs in the 
Ugo province were described by Takimoto.* Silica plays the réle 
of the *“‘binding”’ colloid in most pisolites and is an important con- 
stituent of most iron hydroxide odlites. Siliceous concretions are 
of wide occurrence. Silicic acid is the standard inorganic emulsoid 
sol of the laboratories. 
2. Water: Among the hailstones we find all transitions between 
typical spherulites and spherites of concentric structure’ That 
and from the opening extensive botryoidal surfaces grew up, leaving cavities under- 
neath the crust. Iron chloride, therefore, offers a complete analogy to all the common 
forms of natural gels, especially such as have a tendency to grow crystalline in statu 
nascendi, as, for instance, chalcedony. Ci. F. Cornu and H. Leitmeier, ‘“‘ Ueber, 
analoge Beziehungen zwischen den Mineralien der Opal-, Chalcedon-, der Stilpnosi- 
‘derit-, Haematit- und Psilomelanreihe,’ Zeitschr. fiir Chemie und Industrie der 
Kolloide, IV (1909), 285-90. 
2F. Roth, Allgemeine und chemische Geologie, I (1897), 591, Anm. 
3K. Jimbo, “The Siliceous Odlite of Tateyama, Etchu Province,” Beitr. s. Min. 
Japans, Tokio, 1905, pp. 11-75 (quoted from abstract in Zeitschr. fiir Chemie und 
Industrie der Kolloide, 1V [1900], 287). 
4T. Takimoto, “The Siliceous Oélite of Sankyo, Ugo Province,” Beitr. z. Min. 
Japans, 2 (1906), 60-61 (quoted from Newes Jahrb. fiir Min., etc., I [1907] 197). 
5 According to Schade the coarse layers overlapping onion fashion, frequently met 
with in hailstones, are not equivalent to the exceedingly delicate lamination of true 
odlites, but are due to plastic deformation under external pressure. See Schade, 
Kolloidchemische Bethefte, . (1910), 388; ‘‘Ueber die Koéxistenz des kristallinischen 
und kolloiden Zustandes,” of. cit., pp. 380 ff. 
