404 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Wisconsin, quartzite pebbles apparently from the underlying Penokee 
Huronian. But these occurrences, and the kinds of rocks involved, are too 
few to allow of our very confidently concluding from them the general 
alteration of the Huronian schists prior to the time of Keweenawan depo- 
sition. Pebbles of the older granite and gneiss occur more frequently in 
the Keweenawan conglomerates, so that those rocks must have reached 
their present conditions before the formation of the conglomerates. 
But for the relations of the Keweenawan and supposed Huronian erys- 
talline schists in the basin of Lake Nipigon, subsequently noted, the structural 
relations of the two groups broadly viewed would lead us to the conclusion 
that there was a time interval between the groups sufficiently long to allow 
of erosion to some extent, but not great enough to produce a true uncon- 
formity. On the South Shore, for all the miles between Lake Agogebic, 
in Michigan, and Numakagon Lake, of Wisconsin, the Keweenawan beds 
present a general parallelism in trend and dip to those of the underlying 
Huronian, all being tipped up towards the north at angles which are nearly 
always very high. So far, the appearance is one of complete conformity. 
Looking the other way in this region are the following facts, as I have 
shown in my discussion of the structure of Northern Wisconsin for the 
Wisconsin Geological Reports: 
‘In the Penokee country, the uppermost beds of the Huronian are 
gradually cut out, as we trace them westward, by the gabbro that forms 
the base of the Keweenaw Series—a fact which appears to me best ex- 
plained by the supposition that the gabbro covers and conceals these miss- 
ing beds. West of Lake Numakagon, the diabases and other eruptive 
rocks of the Keweenaw Series appear to completely cover the Huronian, 
in a great overflow. Nevertheless, the approach to conformity in Wisconsin 
is close, and were we to draw our conclusions from this region only, the 
nonconformity could hardly be regarded as proven. There are no such 
undulations in the Huronian of the Penokee district as in Michigan, the 
subordinate members making long and regular bands conforming to the 
general trend of the formation, and also, in a general way, to the trend of 
the several belts of the Keweenaw Series. Moreover, the lessening in dip 
