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Queer flat-lying and many-branching things, which resemble sea-weeds in juiciness and color and consistency, crackle under your feet from time to time; the moist and weighty air seems heated rather from below than from above, less by the sun than by the radiation of a cooling world; and the mists of morning or evening appear to simulate the vapory exhalation of volcanic forces, latent, but only dozing, and uncomfortably close to the surface.
Without obtruding unnecessary technicalities upon my non-professional readers, I may quote the words of Albert Heim as to the conditions as now recognized in these parts: "These flat-lying faults, of which those at Glarus were the first to be discovered, are a universal phenomenon in the Northern and Central Alps."
This example, which was first called the Glarner Double Fold by Escher and Heim, is now universally called a nearly flat-lying "thrust fault," in accordance with the explanations since adopted of similar phenomena elsewhere.
The plateau, consisting of strata but little changed from their original flat-lying attitude, and the platform, developed on rocks of disordered structure made crystalline by heat and pressure, both stand at the common level of the line AB. They are separated by the Appalachian valley, forty miles wide, cut in strata which have been folded and broken into long narrow blocks.
Hence the Piedmont plain as it was before its uplift was not a coastal plain formed of strata spread in horizontal sheets beneath the sea and then uplifted; nor was it a structural plain, due to the resistance to erosion of some hard, flat-lying layer of rock.
Incidentally it may be noted that this very fact that what was long regarded as two completely overturned folds is now spoken of as one flat-lying thrust fault, is prima facie evidence that there is here no physical proof of any real overturning of the strata, such as we do find on a very small scale in true folded rocks.
It was weaker also than the region to the west, since there the sediments were much thinner. Besides, by the long-continued depression the strata of the trough had been bent from the flat-lying attitude in which they were laid to one in which they were less able to resist a horizontal thrust.
These deposits consist of broad, flat-lying sheets of clay and fine sand left by the overflow at time of flood, and traversed here and there by long, narrow strips of coarse, cross-bedded sands and gravels thrown down by the swifter currents of the shifting channels. Occasional beds of muck mark the sites of shallow lakelets or fresh-water swamps.
The rocks in which the canyon is cut are for the most part flat-lying, massive beds of limestones and sandstones, with some shales, beneath which in places harder crystalline rocks are disclosed. Where the canyon is deepest its walls have been profoundly dissected.
We will describe the Algonkian rocks of two typical areas. The formation of flat-lying sandstone which covers this buried land surface is proved by its fossils to belong to the Cambrian, the earliest period of the Paleozoic era.
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