The Bamboo Iron Ore. — li'utchcll. 249 
of depth aiicl physical snrronmling-s, and tliat the waters hcl<l 
considcrahle iron in solution derived from iron-l)earin<^ rocks 
of adjacent land areas. He states in detail the evidence sup- 
porting this hypothesis. But few geologists will question his 
interpretation of the evidence. The idea that the iron ores of 
the lake Superior region have resulted from the metasomatic 
alteration of a "clierty carbonate" on a grand scale, suggested 
hv Irving, lingers in certain quarters to this day. Indeed it is 
the fundamental conception held by the United States geolo- 
gists who hRW labored in the Lake Superior region, although, 
from the force of the evidence, more lately the presence of a 
"green silicate" in the original rock has been recognized as 
an important source of much of the ore. That the iron now 
present in the rocks had its origin in sedimentation, and dates 
from the formation of the rocks themselves, and has simply 
suffered transformation of its chemical composition, resulting 
in different iron minerals, is becoming more and more widely 
proven. This process is one of metamoqjhism, due to the same 
forces tliat have converted many rocks from a state of simple 
sedimentary strata into schists and gneisses. The elements 
were all (or essentially all) present at first. They have taken 
on new forms of chemical combination, and have been locally 
concentrated. The waiter is entirely in accord with Dr. Weid- 
man in this explanation. The author would have found this 
theory applied to the iron ores of Minnesota bv the writer 
thirteen years ago (though with scant recognition of the 
agency of decaying organic matter) had he consulted Ikilletin 
No. 6 of the Minnesota Geological Survey, pp. 103-111.=^ If 
there be any difference between the author's and the writer's 
views it is in relation to the environment of the sedimentary 
action. The author seems to require quiet, shallow water, 
subject to slight, alternating fluctuations of level, but a steadily 
sinking sea bottom, the iron solution in the water derived 
from adjacent land areas. Rather the writer maintained that 
the sea was hot. incapable of supporting organic beings, and 
that the ferric hydrate was a chemical sediment. With later 
observation it has become apparent that hot waters shaded off 
into tepid waters, and that chemical sediment was widely 
•This view was first published in the America.n Gholooist. vol iv dd 
391-300.1889. *^*^ 
