302 J. P. Kimball on Iron Ores of Marquette, Michigan, 
sisted erosion more effectually than the purer schists, and are 
eras in elevated outliers, as seen particularly at the New 
ngland mine, and in the N.W. quarter of Section 21, T. 47 N, 
. 27 W. A specular conglomerate uncontaminated with any 
considerable portion of jasper, forms the bulk of the schists at 
present wrought by the Lake Superior mine. These are jointed 
obliquely, and are cleavable at right angles, to the stratification. 
ecular schist often occurs charged with detrital quartz, or 
sand, thus differing from the conglomerates only in its external 
properties, while it is analogous to them in attitude and actual 
composition, Schists of this description are intercalated with 
the conglomerates in Section 21 above noticed, and in Section 
26 of the same township are found underlying the laminated 
beds which crown the anticlinal arch. 
An estimation of the thickness of the ferriferous series 1s ab 
tended with no little difficulty at present owing to the absence 
of any entire sectional cutting. The Jackson mine presents the 
best data for an opinion upon this point, although its pa 
expose neither the base, nor uppermost members of the series. 4 
is upon the northern dip of a steep anticlinal, and the groundof | 
the quarry is some 500 feet wide, the excavation having 
entirely within the series. At this mine the range of thickness 
exceeds one thousand feet. Individual thicknesses of specular 
schist without the intervention of other schists, are upwards of 
150 feet. Some idea of the massiveness of a homogeneous bed 
of specular schist may be had from the fact that in the month of 
September last 3500 tons of workable ore were thrown down at 
this mine in one blast, for which 11 kegs of powder were used. 
It will be observed that while the smaller plications furnish 
the most available and complete evidences of the stratigr 
ing allowance for superficial vicissitudes, and a large 
denudation. Even if space permitted, I conceive 1 edit 
necessary to multiply instances of this evidence. It has ait 
shown that the iron ores of the Huronian series in Michigan 4° 
which none of the 
precipitation from 
water on the one hand, or by detrital accumulation on the one = 
Fe stificati ticlinal 
They exhibit not only pes Pace of joints 
: hornblende 
f the fer 
riferous series, has already been indicated in general pean av . 
