460 PERSISTENCY AND EQUIVALENCY 
Over this immense tract there is a most wonderful persistence of the rocks, when 
viewed in the aggregate, or by systems. We see everywhere, in the descending 
order, Ist, the Carboniferous; 2d, the Devonian; 3d, the Silurian Systems, of 
Kurope. In details, they are somewhat modified, and different from the European 
subdivisions, and from each other. It is therefore to the discussion of local equiva- 
lents that geologists are now turning their attention. As there is some discrepancy 
in the views of different authors, in regard to the relative age of the lower members 
of the Silurian, in Michigan and Wisconsin, I think this a proper place to add some- 
thing on that subject, based principally on their order of superposition or strati- 
graphy; for their palzontology is still but imperfectly known. 
In the earlier stages of the investigation, the red and variegated sandstones of 
Lake Superior were by some regarded as newer than the new red; by others, as 
older than the Potsdam sand-rock. It is now settled that the Lake Superior sand- 
stones are older than the calciferous sand-rock of New York. But do they belong to 
the same system ? 
Great changes of level have taken place since the deposition of the Lake Superior 
sandstones. The Gros Cap Range has been raised; and the granitic and metamor- 
phic masses on the Canada side; from thence by Mamainse to Michipicoten, to say 
nothing of the great disturbances on the north shore, west of Pigeon River. The 
great central granitic mass, occupying the central parts of Northern Wisconsin, the 
oldest rocks of that State, have been broken, tilted, rent, and modified, by igneous 
action, both metamorphic and trappose. All this, before the uplift of the Kewee- 
naw Trap Range, and at indefinite periods during the deposition of the rocks on 
the Menomonie, Escanawba, and St. Mary’s Rivers. It seems necessary to con- 
clude, that the beds below the Blue Limestone of Cincinnati have, in consequence 
of these changes, or for other sufficient causes, thinned out, and have been replaced, 
so as to destroy the continuity of the strata. The uplifts and revolutions manifest 
at the sources of the Escanawba and Menomonie Rivers, may have contributed to 
such a result. I cannot regard the rock marked by Dr. Houghton as the “Potsdam 
Red Sandstone,” resting upon igneous rocks on the heads of the Chocolate River, as 
the same, or as the equivalent of the lower sandstone of the Wisconsin. Formation 
1, of Wisconsin, now traced to the Oconto, agrees better with the upper gray sand- 
rock of the Pictured Rocks, which is probably not conformable with the red and 
variegated sandstone of Lake Superior, on which it rests. 
The lower magnesian (F. 2), distinctly traced to the Wisconsin River, is either 
wanting on Wolf and Oconto Rivers, or has become siliceous, so as to answer better 
to Dr. Houghton’s “ Calciferous Sand-rock,” occupying a belt of fifteen to eighteen 
miles wide on the Escanawba, twenty miles from its mouth. In the absence of 
fossils, I am inclined to call the calcareous sand-rock of the Oconto Falls, the “ Lower 
Magnesian Limestone.” If the Blue Limestone of Cincinnati is represented there by 
the marls which exist near the level of Lake Winnebago, it would strengthen this 
conclusion. For between the bluffs of Wolf River, in Township 22 north, and the 
Neenah quarries and exposures at Grand Chute, is but twelve and fifteen miles, on 
the line of dip within which space we must look for the Lower Magnesian Lime- 
stone. if it exists. The calciferous sand-rock of the Escanawba, which T have sur- 
