The Bamboo Iron Ore. — JVincliell. 247 
quartzvte which appears on the Minnesota river a few miles 
south of Glencoe, which has been without exception paral- 
lehzed with the Baraboo quartzyte, but it may be a quartzytc 
stratum separated from tlie main quartzyte Ijy a stratum of 
red shale. In several cases such interstratified shale beds have 
been observed. The pipestone, or catlinyte, layer at Pipe- 
stone, Minnesota, is a familiar instance. Indeed, the New 
Ulm quartzyte itself is rather slialy than quartzitic in its lower 
layers and the red color is to a larg-e extent, a superficial 
feature. The outcrop of the underlying conglomerate is so far 
removed from the quartzyte outcrop that intervening room 
exists for a great thickness of shale or shaly quartzyte. 
The iron ore of the formation (hematite and siderite) is 
somewhat different from all the iron ore deposits of the lake 
Superior region in its mineralogical associations. The chief of 
these differences consists in the presence of a large amount of 
dolomite. This carbonate develops into important strata 
which, being crystalline, are denominated marble. ]\Iuch of it 
is aft'ected by the presence of iron, and sometimes by manga- 
nese. The general term ferrodolomite is usually applicable. 
The iron ore grades into this rock, and also into ferruginous 
chert, and into ferruginous slate by insensible changes, re- 
sembling in all respects the gradations seen in sedimentary 
rock from one to another. The workable ore occurs at dift'ercnt 
horizons, the deposits being conformable with the strata, vary- 
nig from thirty feet thick to two hundred feet, in the form of 
more or less elongated lenses. The author remarks that this 
ore deposit has more similarity to the ores of post-Cambrian, 
such as the Clinton ore, than any of the known ores of the 
lake Superior region. Still, notwithstanding these differences, 
there are greater bonds of alliance wdth the other ores of the 
lake Superior region by reason of which this ore can be class- 
ed, with strict propriety, with the well known ores of the 
Northwest. The chief difference, above noted, is one further- 
more that does not always obtain, for in the eastern end of 
the Mesabi iron range the iron horizon is accompanied by a 
deposit of ferro-dolomite or dolomitic siderite which constitutes 
a noteworthy stratum in the base of the Animikie.* and its 
origin and significance have been discussed by the writer. 
• Final Report of the Minnesota Geological Surrey, pp. 312, 638, 997. 
