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Updated: June 21, 2025
On passing this line, and continuing towards the S.E., the formations 4, 3, and 2, are again repeated, in the same relative order of superposition, but with a southerly dip. These are composed of red conglomerate and sand, and are newer than any of the groups, 1, 2, 3, 4, before described, and rest UNCONFORMABLY upon strata of the sandstone group, No. 2.
Then, after a vast interval, there comes a break: something like an end and a new beginning, as if one day of creation were finished and a new one begun. The different formations lie unconformably upon each other, which means revolution of some sort.
This whole pile resembles, but not very closely, some of the less brecciated parts of the great porphyritic conglomerate formation of Chile; but it does not probably belong to the same age, as the porphyries here rest unconformably on the altered feldspathic clay-slate, whereas the porphyritic conglomerate formation alternates with and rests conformably on it.
In some places this bed of pebbles even intersects the mass of the clay, giving it in such instances an unquestionably stratified character. There can be no question that this more recent formation rests unconformably upon the sandstone beds beneath it; for it fills all the inequalities of their denudated surfaces, whether they be more or less limited furrows, or wide, undulating depressions.
Then the edges of the old red sandstone were eaten away by the sea and some think by ice too, in some earlier age of ice; and then the limestone coral reef was laid down on them, "unconformably," as geologists say just as you saw the new red sandstone laid down on the edges of the limestone; and so one world is built up on the edge of another world, out of its scraps and ruins.
With the exception of the grauwacke being here more abundant, and the clay-slate less altered, this formation closely resembles that unconformably underlying the porphyries at the western foot of this same range; and likewise that alternating with the porphyritic conglomerate in the main Cordillera.
An erosion surface which thus parts older from younger strata is known as an UNCONFORMITY, and the strata above it are said to be UNCONFORMABLE with the rocks below, or to rest unconformably upon them. An unconformity thus records movements of the crust and a consequent break in the deposition of the strata.
By the banks of a deep gully here the rocks are well exposed: they consist of soft clay shales resting on the limestone, which is nearly horizontal; and this again, unconformably on the quartz and hornstone rocks, which are confused, and tilted up at all angles.
The first of them, that of Utznach, is a delta formed at the head of the ancient and once more extensive lake. The argillaceous and lignite-bearing strata, more than 100 feet in thickness, rest unconformably on highly inclined and sometimes vertical Miocene molasse.
They may be forming at all periods; but before any of them can become visible, they must be raised above the level of the sea, and some of the rocks which previously concealed them must have been removed by denudation. The Upper Laurentian or Labrador series lies unconformably upon the Lower, and differs from it chiefly in having as yet yielded no fossils.
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