iS rite treet, , Maal 
R. Irving—Copper-bearing Rocks of Lake Superior. 51 
consin, they appear to dip underneath* the lighter-colored Lower 
Silurian sandstones of the Mississippi Valley, of which they 
are probably merely the downward continuation ; thus showing 
the same relation to newer rocks as do the sandstones of east- 
ern Lake Superior. (3) Similar lithological characters, an ad- 
missible test, I suppose, for whi so close to one another, and 
for entirely undisturbed roc 
At the two points, aad ure, in Ashland County, are ex- 
posures of dark-red sandstone, and sandy shale dipping seen 
as shown on the section. At one of these points, 
easternmost, there is exposed a thickness of at least 2, 000 rae 
of sandsone, dipping southward, at an angle of 38°. This 
great thickness is actual and not due to faulting. The impres- 
sion that these sandstones, exposed at points more than ten miles 
apart, are portions of the northerly edge of a synclinal, of which 
the vertical sandstones to the south form the southerly, is almost 
irresistible, This opinion is strengthened by (1) the difficulty of 
accounting for so great a thickness with so uniform a disturbance, 
at points | more than ten miles apart, by ee this distur- 
bance to a mere dislocation of the Silurian sandstones, which oc- 
cur horizontal only a few miles off ; (2)the occurrence oof horizontal 
sandstones within the jaws of the su apposed: synelinal; (3) the 
very great thickness of these beds, which allies them closely to 
the vertical beds on the southward, whose total thickness can- 
not be less than 10,000 feet; (4) the occurrence of trap at the 
point marked 111 ¢, a little to the north of the line of the southward 
dipping sandstones ; and (5) the probability, alluded to farther 
on, that there is somewhere in this region of Wisconsin a 
synclinai, representing the westward continuation of that exist- 
ing between Keweenaw Point and Isle oyal 
Following the shore of Lake Superior westward from the 
Apostle Islands, the horizontal sandstones can be traced with- 
out break until Douglas County is reached, when they disap- 
pear from the coast—which is here altogether of red clay marls—. 
but appear constantly in the beds of the many streams flowing, 
northward into the lake. On ascending these streams to the. 
southward, the red sandstones can be traced to their junction: 
with the trappean beds of the Copper-bearing Series, which, 
here dip, wherever the dip is observable, at a comparatively low, 
angle to the south. The sandstone beds continue horizontal, or: 
with a very slight dip northward, to within a short distance of 
the trap, when, in most pcan they show a remarkable — 
change. In one case, however, they continue to within: 
ibagr J feet of the trap sions change, the exact. june-: 
tion being concealed by an eroded gulley. At Black River, 
for three hundred feet from the trap, the sandstone is broken up, 
* D. D. Owen, Report on the Geology of Iowa, Wisconsin, and Minnesota. . 
