i'2'2 The American Geologist. Jane, 1894 
It is by Swedes and Americans, and partly also by German investiga- 
tors, that ii lias been shown tliai the extensive iron ores of the Cambrian 
and upper pari of the Archean are of sedimentary origin. This con- 
clusion rests upon the following facts: 
1. Tlie ores are always parallel wit 1 1 the bedding and participate in 
all folds and flexures. A general Strike contrary to that of the rocks 
has not been proven. 
2. The ore deposits are bedded in a typical manner, consisting prin- 
cipally of a series of abruptly changing layers, chemically and miner- 
alogically in strong contrast. 
'■',. Each single rock series, or each stratigraphic horizon, is charac- 
terized by a definite type of iron ore bed. 
4. The ore deposits occur in close connection with beds of limestone 
and dolomite, which are of rare occurrence, especially in the Archean. 
5. They form a limited class, well characterized mineralogically, 
and still better chemically, by the metal-combination Fe and Mn, which 
can be sharply distinguished from the group of ore deposits formed by 
processes of emanation (containing chiefly Cu, Ni, Co, Zn, Pb, Ag, Sn, 
Fe. etc. ). 
6. One definite class of iron ore deposits, viz., the basic and at the 
same time manganiferous ore, is often marked by the presence of graph- 
ite or organic matter: and in some Archean ore deposits of the United 
States we even find a combination of sideriteand carbon or organic mat- 
ter, corresponding to the ; 'Kohleneisenstein" or blackband ironstone. 
~. In all the younger formations undoubtedly sedimentary iron ore 
deposits occur (e. "'. meadow, lake, and bog ore, at the present time: 
oolitic iron ore, of the Jurassic: blackband ironstone, in the Carbonifer- 
ous). A priori we should expect to find corresponding deposits in the 
oldest sediments. 
8. In conclusion, il may also be mentioned that this class of iron ore 
deposits, unlike the majority of ot her ore deposits, has no direct connec- 
tion with any eruptive rock. 
That these iron ores cannot be supposed to be intrusive eruptive sheets 
needs no further proof. It may be attempted to prove that the ores un- 
der discussion were formed by. pneumatolytic processes. As the mosl 
important support for this theory, it must be shown that our ores, min- 
eralogically as well as structurally, are distinguished partly by the 
identical mineral combinations (garnet, epidote, differenl augites, and 
vesuvianite and scapolite, as exceptions), which would be produced in 
the limestone and calciferous schists by contact metamorphism. as 
well as by metamorphism accompanied by pneumatolytic processes. It 
may however be mentioned that the latter minerals belong to almost 
any primary limestone, whether it be accompanied by ir re beds or 
not. That is, the minerals are formed not only as a result of that spe- 
cial contact metamorphism, but also as a result of that general meta- 
morphism which the Archean formations have undergone. Further- 
more, that very siliceous mineral, viz., quartz, which is most abundant 
in our iron ores, does not belong to the group of minerals formed by 
