JUNE, 1906. NEw Forms oF CONCRETIONS—NICHOLS. a4 
large dilution of the solvent when removed from the immediate 
vicinity of the decaying root or leaf which is the : ource of its supply. 
Such small limonite-sand concretions forming near the surface 
of semi-fixed dunes are, therefore, due to an action of vegetation upon 
the limonite coatings of the sand grains of the dune, an origin not 
unlike that of the bog and pond limonites. 
LIMONITE GEODES, MUSCOGEE, INDIAN TERRITORY 

A series of limonite geodes (Museum No. G. 1308) of unusual 
character was presented to the Museum by General G. Murray Guion. 
According to General Guion the geodes are found in clay in the bottom 
of a “‘draw”’ or ravine at Muscogee, Indian Territory. These spec- 
imens are composed essentially of limonite with turgite and consist of 
a crust, a core and acentral cavity. They are of the irregular discoid 
form with smooth exterior which characterizes a common type of 
siderite nodule. They are of moderate size. A typical specimen 
(Plate XXIV, Fig. 4) weighs 270 grams, has a diameter which varies 
from io to 12 centimeters and a thickness of 4 centimeters. When 
the specimen hes flat its horizontal projection is a decidedly irregular 
oval. All vertical projections and sections are ovals, slightly irregular 
but symmetrical with respect to the major diameter. Some specimens 
possess th cker and some thinner forms than this. The surface is 
smooth except for such roughness as is due to scaling of the lamellar 
crust. The color is light gray with dark brown stains. Some 
Specimens are coated with a firmly adherent yellow ochreous clay in 
which they appear to have been imbedded, while many specimens 
are perfectly free from this coating. The specimen shown in the 
illustration s enclosed in a light-colored laminated crust. Inside the 
crust and sharply separated therefrom, is the main portion of the 
geode, a hard, red and yellow, concentrically banded, agate-like mass 
of limonite and turgite. The center is occupied by a small cavity 
which varies in shape and size in different specimens, and suggests in 
outlines the central cavity often found in agates. 
The shell is from 3 to 7 millimeters in thickness. Its external 
color is gray to brown; fractured surfaces are ight gray with dark 
brown and limonite yellow areas. The outer portion of the crust is 
almost universally light gray, wiile the inner parts contain more 
of the darker areas. | 
The crust is strongly laminated, especially in the outer portions. 
The individual laminae, which are somewhat under a millimeter in 
