246 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
and importance in its bearing upon the structure of the western termination 
of the Keweenawan trough, as is shown in a subsequent chapter. 
The exposures of Huronian schists on the upper Kettle River, taken 
together with those at Moose Lake, on the Saint Paul and Duluth Railroad, 
and those at Thompson, on the Saint Louis River, are also of great interest, 
since they form a line beyond which it is certain that the Keweenawan rocks 
cannot pass to the westward. 
Upper Saint Croiz.—For 30 miles above the mouth of the Kettle River 
the Saint Croix shows no rock of any kind. Then come large exposures of 
southeastward-dipping sandstone, extending for many miles along the stream. 
I quote in this connection from Professor Chamberlin’s description :* 
From See. 4 (I. 43, R. 13 W.) to the southern line of the county? (Sec. 33, T. 43, R. 
14 W.), the bed of the stream? is almost continuously composed of sandstone and con- 
glomerate. The greater portion of this is the common red sandstone of the series. 
The lower mile and a half is conglomerate, and probably corresponds in stratigraphical 
equivalence to the conglomerates of Sees. 27 and 14, T. 44, R. 13 W., above-described, 
as it lies in the line of strike, and bears a similar relation to the crystalline strata on 
the northwest. By consulting the map, it will be seen that from Chase’s dam to the 
county line, a distance of about 11 miles, the river runs an almost direct course, and 
with slight interruptions is bedded on sandstones and conglomerates. A casual glance 
will show that the stream runs closely with the strike of the strata. A more careful 
study makes it appear that the river crosses the strata at a very small angle, passing 
from higher to lower beds. Near the county line, however, the river turns southward 
and pursues, for about three miles, a southerly course. This brings it over higher (geo- 
logically) strata. For a little more than a mile, however, it is bedded in drift, but 
near the north line of Sec. 9 (T. 42, R. 14 W.), the sandstone of the series reappears 
in the bed of the river and extends across it, causing rapids and forming occasional 
low exposures in the banks. The ledges show fine ripple-marks and occasionally rain- 
drop impressions. They are more indurated and seem to contain more quartz and less 
argillaceous material than those previously described. This sandstone again becomes 
concealed at the south line of the section, but reappears in the bed of the river in the 
Indian village in the N. W. 4 of the N. W. 4 of See. 21, (T. 42, R. 14 W.), about a mile 
below. These are probably the highest beds of the Keweenaw group exposed in the 
district. 
Next immediately underlying this sandstone and conglomerate series, so far as the 
outcrops show, there appears to be a diabase, little exposed, underlaid by a stratum 
of easily-recognized melaphyr, forming at the surface outcrops along a belt lying 
parallel to the sandstones. This is the typical Keweenaw melaphyr described by 
1Geology of Wisconsin, Vol. III, p. 424-427. 
2? Douglas County, Wisconsin. 
The Saint Croix. 
