28 The American Geologist. J"'y' ^^"i- 
Description of the Ore. 
Pronounced variation in the i^hysical features and appear- 
ance of the ore is a prevailing- characteristic, though it usually 
has a marked pisolitic structure. The ore varies in color from 
\.hite and cream through pink to a deep red in which iron ox- 
ide is present as an essential constituent, and at times the iron 
oxide is equal to and may even exceed the alumina. The 
pisolitic type consists of concretions and matrix in nearly all 
proportions. The ore varies from a structureless bauxitic 
clay, without trace of the pisolitic structure shown, through 
the pisolitic type in which concretion and matrix are in about 
ecjual proportions, to the pebble type, which consists of con- 
cretions averaging three-quarters to two and one-half inches 
in diameter, held together by a soft and plastic puttv-like clay. 
The matrix varies in hardness from a soft plastic clay-like 
material to a dense and compact form, which breaks with a 
sub-conchoidal fracture ; not scratched by the nail but readily 
scratched with a knife. It ranges in color from white and 
cream to the highly ferruginous deep red types, the cream- 
colored and dull gray tones being perhaps the most common. 
The pisoliths or concretions are nearly spherical in shape and 
range in size from the smallest Dea up to two and one-half 
inches in diameter. The concentric structure is characteris- 
tic ; the layers rarely exceeding a knife's-edge in thick- 
ness and are seldom homogeneous in color but usually 
alternate from white through intermediate shades to red. They 
may be hard and compact from centre to circumference break- 
ing with a conchoidal fracture ; or, as is more often the case, 
the hard outer layers may contain a powdery interior, red or 
white in color, and not filling the entire space or cavity — a 
condition probably due to- subsequent shrinkage from dessica- 
tion. The pebbles mav be single or compound in structure ac- 
cording to whether they are comoosed of a single neucleus or 
of several nuclei. 
With reference to structure the following types of the ore 
have been distinguished by Hayes :* (i) pebble, (2) pisolitic, 
{^') oolitic, (4) vesicular, (5) amorphous. In well differen- 
tiated portions of the ore the above types are easily recognized, 
Ijut the classification is purely arbitrary since the various types 
*Op. cited, pp. 562-564. 
