The Late Minnesota Survey. — Winchell. 249 
nesota. It is the western representative of the Potsdam sand- 
stone, of Potsdam, N. Y. The light-colored friable sandstones, 
both in New York and in the Mississippi valley, lie higher, and 
are allied to the Calciferous, lately called Beekmantown. The 
eruptive disturbances which immediately followed this sand- 
stone in the lake Superior region, causing the widespread non- 
conformity of the lately friable sandstones, were wanting in 
the Adirondack region. Hence the difficulty of separating 
this quartzyte from those later sandstones in the northern 
part of New York state. This quartzyte seems to be the rep- 
resentative of the Middle Cambrian, as the Beekmantown is of 
the Upper Cambrian. 
(9.) The final conclusion of the Minnesota Survey as to 
the origin of the ]\Iesabi iron ores refers them to a greensand, 
which has been altered, affording iron ore by concentration 
of the iron in certain favorable positions. Cotemporary with 
this alteration was a concentration of silica, and this was in- 
creased by oceanic precipitation. The original greensand was 
found to become pebbles, and to increase into angular masses 
that were neither sand nor pebbles, but rather breccia. These 
breccia masses have at first an amorphous crystalline texture 
and grade into a form of the iron-bearing rock which was 
named taconyte, and the whole was referred to volcanic action, 
being different forms of suddenly cooled volcanic glass and 
rhyolyte, broken and distributed by beach action. While this 
volcanic debris was undergoing this transformation great quan- 
tities of silica were set free from the glass, but this silica im- 
mediately saturated the debris producing spotted jasperoid 
taconyte and sedimentary jaspilyte. (No. 2 below.) 
Having reached this result on the Mesabi range it opened 
the door to the understanding of the iron ores of the Vermilion 
range, and at once the rhyolitic forms and all the igneous as- 
sociations of those ores with basic igneous rock, were eluci- 
dated, thus confirming Wadsworth's idea of the igneous origin 
of the jaspilytes of the Marquette region — rather the igneous 
origin of the rock which later was changed into jaspilyte. 
Here a few words of caution arc necessary. There are 
three rocks which mav be called jaspilyte, and have been so 
called. 
(i.) The rock al)ove described, the result of silicification 
of basic rhvolvtes and olisidian. 
