ORIGIN AND CLASSIFICATION OF ORE DEPOSITS. 167 
2. Ore disseminated through strata; as copper in the schists of Mansfeldt 
and in the sandstones of Lake Superior. 
1. Segregated masses in strata; as sheets of copper in the Lake Superior 
sandstones; balls, kidneys and sheets of clay ironstone in the shales of the Coal 
measures, etc. 
UNSTRATIFIED DEPOSITS. 
These have been divided into: 
Eruptive masses. 
Disseminated through eruptive rocks. 
Contact deposits. 
Stockworks. 
Fahlbands. 
Impregnations. 
Chambers. 
Mineral veins. 
Of Eruptive masses of metalliferous matter I must confess myself incredu- 
lous. Examples of these are cited in the crystalline iron ores of the island of 
Elba, those of Nijni, Tagilsk in Russia, and in Sweden, and even the iron ore- 
beds of Lake Superior and Missouri. As late as 1854, this was the view taken 
of our crystailine iron ores by Whitney in his Metallic Wealth; but great advances 
have since been made in our knowledge of these deposits, and it is now generally 
conceded that all our crystalline iron ores are simply metamorphosed sedimentary 
beds. The evidence is accumulating that those of the old world have the same 
character. Professor Otto Torell, the Director of the Geological Survey of 
Sweden, recently told me that he had visited all but one of the iron districts of 
Sweden, had found that in all these the iron ores were metamorphic, and he had 
no doubt that those yet unexamined were of similar nature. Where metamorphic 
action has been peculiarly violent, the beds of iron ore have been more or less 
disinembered, and perhaps in some instances have been actually fused; but that 
any bed of iron ore.is the result of an eruption from the interior of the earth, 
is scarcely to be credited. 
The examples of the occurrence of metalliferous matter disseminated through 
eruptive rocks are by no means uncommon, and the amygdaloid traps of Lake 
Superior, in which the cavities formed by gases have been more or less perfectly 
filled with copper, suggest themselves at once. Pyrites, magnetic iron, and 
platinum are found sparsely diffused through trap-rocks, and are sometimes con- 
centrated in such a way as to form valuable deposits when the trap decomposes. » 
Contact deposits are usually understood to be accumulations of metal or ore 
along the planes of contact between two strata; and the sheets and strings of 
copper which are concentrated at the junction of the trap and sandstone in some 
parts of the south shore of Lake Superior constitute illustrative examples of this 
class of mineral deposits. There is, however, considerable diversity in character 
among the deposits grouped under this head; the chief distinction being that 
OI ARR SH 
