14 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
line form by reason that a large number of crystal units started 
growth in a narrow space, and the mutual interference during growth 
has compelled growth to take place all in one direction, resulting in 
radial-fibrous spherical bodies. The exteriors of such bodies are 
usually covered with euhedral terminations of the crystals making 
up the spherical mass. A study of the Spokane siderites from this. 
standpoint leads to the conclusion that the iron carbonate was in 
colloidal form when deposited, a conclusion sustained by the per- 
fectly spherical form taken by a majority of the nodules, their entire 
homogeneity, lack of concentric rings, fineness of fibrous structure, 
and the absence of crystal terminations on their exterior. On the 
other hand, the apparently third-generation drusy crust on the 
siderites of one nodule was doubtless deposited in crystalline form. 
The sphaerosiderite variety of iron carbonate is known from a 
number of localities in Europe, but no previous locality comparable 
to these European occurrences has been found in the United States. 
At Felsobanya in Hungary typical spherical bodies of siderite occur 
in veins with ore minerals, but the typical European occurrences 
are, like the one at Spokane, in vesicles in basaltic rocks. A speci- 
men in the National Museum from Steinheim, Hesse, Germany (Cat. 
78,837), is so similar to those from Spokane as to be indistinguishable 
without microscopic examination of the enclosing rock. 
FERRICALCITE. 
One specimen, which when received was labeled ‘‘ Pseudomorph 
after siderite,”’ consists of the dark-colored opalized rock containing 
a cavity of the usual type lined with the ferric opal. In this cavity 
is a single roughly spherical nodule about 17 mm. in diameter, which 
has a light buff color and velvety surface. When fractured, the 
interior is white, compact, dense-fibrous, and tough. Fragments 
dissolve quickly with effervescence in cold dilute hydrochloric acid. 
Upon standing in the air fresh surfaces begin to turn buff imme- 
diately. OC. S. Ross, upon microscopic examination found this ma- 
terial to have optical properties intermediate between those of calcite 
and siderite, and it is evidently an intermediate lime-iron carbonate. 
It is not probable that this represents a replacement of an original 
siderite nodule, but it more probably represents local variation in 
the composition of the carbonate-depositing solutions. It is possible 
that it represents an outer deposit and that a nodule of the ordinary 
siderite is enclosed within the ferriferous calcite nodule; but this 
could not be determined without destroying the specimen, which is 
the property of the Eastern Washington State Museum. 
OPAL. 
At least two varieties of opal are abundantly present in the speci- 
mens. The first of these, which has been referred to as iron opal, 
