I'lic liarabot) Iron Ore. — JVinclicll. 245 
ed by Salisbury and AtwiHid, is synclinal and the thickness of 
the formation less than half as much as calculated by the other 
geologists. The writer has a personal satisfaction in this re- 
sult, since, in several general discussions of the geology of the 
Nortinvest he has compared the liaraboo region with thd 
geology of Minnesota and has insisted that the l>araboo 
(luartzytc is later in date tlian the Kewcenawan cpiartz porphy- 
ries and later than the Animikie iron ore, on the ground that 
its Minnesota representatives are found unquestionably to oc- 
cui)y sucli a stratigraphic position. I'roni several calculations 
the author derives an average result for the thickness of the 
Baraboo quartzyte, viz : between 4000 and 5000 feet, without 
allowing for any faulting. This result is ])robably too high, 
since it is not likely that there is an absence of such move- 
ments, or even of profound faulting, such as would cause an 
elongation of the surface exposure and hence an elongation of 
the hypotenuse of the triangle of dip. Probably these fig- 
ures, reduced fifty per cent, would more nearly express the 
actual thickness. 
Above the quartzyte is the Seeley slate, which is known 
only by underground exploration, having no surface outcrops. 
By mining operations and drilling it is traceable along the 
north side of the south quartzyte range a distance of six or 
seven miles. It is gray, cleaved somewhat like roofing slates, 
and so soft that it can gcnerallv be whittled with a knife. It 
is a sedimentary rock and its petrographic description and 
composition indicate that it is not free from volcanic elements. 
Indeed, its reference largely, or wliolly, to the agencv of 
igneous action, a sedimented volcanic ash containing more or 
less of other detritus, would be in keeping with the cliaracters 
given to it b\- Dr. W'eidman. In that case it is a rotted igneous 
ash modified by sedimentary elements. The fact tliat it shows 
commonly a well developeil diagonal slaty cleavage implies 
(litTl'erential pressure and shearing in the fomiation, such as 
would materially affect any calculation of its thickness unless 
it be allowed for, as above suggested for the ([uartzyte. Tlie 
thickness of this soft shaly slate is ])lace<l by the author at 500 
to 1000 feet, but it may be considerably more, as only the 
roughest estimates can lie made. In Minnesota this slate, or 
what lies above the great quartzyte, is well known, having 
