The Superior Oldland.An outlying upland of the Laurentian highlands of Canada projects into the United States west and south of Lake Superior.
It is of greater altitude (Mt Marcy 5344 ft.) and of much greater relief than the Superior Oldland; its heights decrease gradually to the north, west and south, where it is unconformably overlapped by Palaeozoic strata like those of Minnesota and Wisconsin; it is of more broken structure and form on.
Region of tile Great LakesThe Palaeozoic strata, already mentioned as lapping on the southern slope of the Superior Olclland and around the western side of the Adirondacks- are but parts of a great area of similar strata, hundreds of feet in thickness, which dec]ine gently southward from the great oldland of the Laurentian highlands of eastern Canada.
Inasmuch, however, as the floor on which the overlapping strata rest is, like the rest of the Laurentian and Superior Oldland, a worn-down mountain region, and as the lowest member of the sedimentary series usually contains pebbles of the oldiand rocks, the better interpretation of the relation between the two is that the visible oldiand area of to-day is but a small part of the primeval continent, the remainder of which is still buried under the Palaeozoic cover; and that the visible oldiand, far from being the first part of the continent to rise from the primeval ocean, was the last part of the primeval continent to sink under the advancing Palaeozoic seas.
When the oldland and its overlap of stratified deposits were elevated again, the overlapping strata must have had the appearance of a coastal plain; but that was long ago; the strata have since then been much eroded, and to-day possess neither the area nor the smooth form of their initial extent.
As in all such forms, the Niagara cuesta has a relatively strong slope or infacing escarpment on the side towards the oldland, and a long gentle slope on the other side.
In Wisconsin the inner lowland presents an interesting feature in a knob of resistant quartzites, known as Baraboo Ridge, rising from the buried oldland floor through the partly denuded cover of lower Palaeozoic strata.
In the oldland area, independent of the overlap of Palaeozoic strata.
Within the Superior oldland area; but there is at present no direct evidence in favor of this hypothesis.