igos.] CHANCE— THE ORIGIN OF BOMBSHELL ORE. 137 



and workmen report finding many of them filled with water. Some are 

 filled with clay, which still retains the laminated structure and appearance 

 of the original slate from which the clay was derived, furthermore, the 

 slaty structure was found to extend through the ore shell, which showed, 

 besides the plain lamination of slate, a faint concentric structure as well. 

 . . . While only one shell was found still retaining the laminations of the 

 clay, there were many others containing clay and sand. Some of the shells 

 were but thin crusts, while others were quite thick, almost solid ; some have 

 a smooth, velvety or bright mammillated inner surface, frequently coated 

 with manganese oxide. In some instances the lining of the shell is covered 

 with many small stalactites of ore. . . . Many of the shells are lined with 

 a dense fibrous layer, often an inch or more in thickness. . . . The thinner 

 shells have all been broken, and we see only the fragments of them in the 

 clay-ore masses. This shell form of ore . . . forms an appreciable part 

 of the ore body in many cases. The small, irregular, nodular-like pieces of 

 ore, commonly knows as shot ore, are presumably closely related in origin 

 to the shells. . . ." 



The inner wall of many bombs consists of a hard, bright, brown 

 or jet-black, glazed surface, curved, rounded or botryoidal. This is 

 frequently described as a manganese coating, but is doubtless a film 

 of iron or manganese silicate. Occasionally the interior or a part 

 of the interior is lined with a layer of extremely hard, flinty, liver- 

 colored iron silicate, or with quartz crystals or chalcedony, and the 

 same silicate frequently forms a considerable portion of the body of 

 the shell or of its outer layers, but generally the shell is composed 

 of high-grade limonite, of a fibrous structure, especially in those 

 layers forming the inner lining of the shell. 



These peculiarities are satisfactorily accounted for neither by the 

 theory that these ore masses owe their origin to concretionary action, 

 nor by that which assumes the direct deposition of ferric hydrate 

 upon the interior of rock (limestone?) cavities. They may, how- 

 ever, be explained by assuming that the bombs are the residual 

 masses, remaining after oxidation, of iron sulphides or carbonates 

 containing sand or clay or both in varying proportions. 



If the material from which this ore is formed consists of sand- 

 stone, or of sandy slate, or of clay slate, impregnated more or less 

 completely with pyrite or siderite, the formation of bombshells, con- 

 taining just such materials as are found in these shells, may be 

 readily explained, especially if the iron impregnation be in the form 

 of pyrite or marcasite, that is, FeS.. 



