1880,] 473 [Wadsworth. 
eruptive deposits of iron exactly at this point. It is well known, as 
remarked by Prof. J. D. Whitney, if iron ores were more valuable 
than they now are, numerous dikes of basaltic and other eruptive 
rocks exist that would be worked for the iron ore they contain. We 
hold that as it is, such dikes have been and are now being worked, 
only their origin is denied. 
In the case of the eruptive rocks the iron is in the state of hema- 
tite and magnetite, while it is necessary, if we adopt the bog theory, 
that the limonite should be transformed into hematite and magnetite 
in some unknown way. In the eruptive rocks the iron ore, except in 
places, is subordinate to the remainder of the rock; and in the Mar- 
quette district the ore is likewise subordinate to the jaspilite. 
Let us again enforce the principle : whether the Marquette ore 
and jaspilite were formed as eruptive or sedimentary masses can only 
be told by studying them and seeing if they have the characters of 
bog ore or of eruptive rock. In this way only are we able to connect 
their present state with their past. It is not proper to begin with 
any of the modern formations of iron and theorize back until we 
reach the older ones, claiming that we have thus proved the way in 
which the older ones must have been formed. If our logic and sci- 
ence are correct in this a priori method, we simply show how the ore 
might, not must, have been produced. The must comes only from the 
study of the state of the ore and its relations : facts to which all the 
theories must conform. Again, we remark, we are not to be taken as 
advocating the eruptive origin of all deposits of iron as others do the 
sedimentary origin of all, but merely of such as we think show evi- 
dence of the former origin. Such ores as show internal and external 
evidence of sedimentary deposition we accept as sedimentary. 
2°. The banding and lamination of the jaspilite and ore do not 
appear to us to be proof of sedimentary origin, since a similar band- | 
ing is strongly marked in the rhyolites the modern lavas approaching 
nearest the jaspilite, in dikes of felsite, in furnace slags, etc. Allow- 
ance, too, has to be made for the alterations that have been produced 
in the rock since its consolidation. This structure is common to 
both sedimentary and eruptive rocks, hence per se is of no value 
either way. ‘The structure of the banding does often show the ori- 
gin of the rock when it has been studied with care. Those advo- 
cating the sedimentary origin of the above-mentioned ore have 
rested their claim on the simple fact that the rock was “ striped,” 
and not on the character of the banding. We have studied the band- 
