598 WALTER H. BUCHER 
7. Siderite: Siderite is occasionally found in spherulitic form in 
cavities of basalt (spherosiderite).! Dana, Naumann-Zirkel, and 
others mention the existence of odlitic siderite. The only descrip- 
tion of such an occurrence that has come to my attention is that 
of a specimen described by Dewalque from the Belgian coal meas- 
ures.? Sideritic concretions (“clay ironstone’) are commonly 
associated with caustobioliths. 
This association is significant, since a colloid form of siderite 
was described by Van Bemmelen from the upland bogs of the Dutch 
province Drenthe, where it is found in the form of concretionary 
masses in irregular distribution in the peat. 
North of Preston, in Bath County, Kentucky, the Devonian 
limestone, which normally is dolomitic and more or less cherty, 
is partly replaced by a siderite. A specimen of the ore, presented — 
to me by Dr. A. M. Miller, shows numerous small o6litic grains 
(o.5 mm. in diameter) of a light green silicate, uniformly distributed 
through the dark brown rock, which, under the microscope, exhibit 
a delicate concentric structure, rather indistinct in some grains 
(Figs. 1 and 2). The surrounding groundmass offers the usual 
appearance of interlocking siderite crystals. But at, the contact 
with the odlites the siderite crystals show the sharp outlines of 
perfect rhombohedrons extending into the body of the odlites 
without disturbing their concentric structure. In this remarkable 
case the silicate odlites apparently formed in free suspension in a 
matrix which must have been an amorphous mud or a gel of iron 
carbonate, which later crystallized out before the odlites had lost 
their gelatinous character. 
The necessary reducing conditions under which this local deposit 
originated within the coral-bearing dolomites of the Onondaga Sea 
may have existed in a depression on the bottom of the shallow sea 
in which the water lay stagnant,‘ or in a lagoon, which would not 
seem improbable if the assumption of a large island or peninsula 
t As, for instance, at Steinheim, Hessia, where the author had occasion to observe 
and collect it. 
2G. Dewalque, Ann. d.1. Soc. géol. d. Belg., XV, Bulletin (1888), p. Ixxx. 
3 J. M. Van Bemmelen, Zeitschr. fiir anorg. Chemie, XXII (1899), 313. 
4See, for instance, J. Murray and J. Hjort, The Depths of the Ocean (London, 
1912), Pp. 257. 
