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On examination, I found them to have been shaped by the hand of man, but so weathered out and changed by the slow process of atmospheric erosion that the evidences of art were almost obliterated. The openings are arched irregularly above, and generally quite shallow, being governed very much in contour and depth by the quality of the rock.
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.
But since that remote time the upfolded mountains had been worn to plains and hilly uplands, the remnants of whose uplifted erosion surfaces may now be traced along the western mountain slopes. Beginning late in the Tertiary, the region was again affected by mountain-making movements.
On the one side erosion has since stripped off the sandstones for the most part, but the hard crystalline rocks yet stand in bold relief. On the other side the weak sedimentary rocks have been worn down to lowlands.
Those vast sloping taluses are as clean as a meadow; rarely at the foot of the huge vertical walls do you see a fragment of fallen rock. It is as if the processes of erosion and degradation were as gentle as the dews and the snows, and carved out this mighty abyss grain by grain, which has probably been the case.
The result of this erosion and transportation has been to change the conditions of the surface both as regards soil and drainage. As the reader has doubtless perceived, ordinary soil is, outside of the river valleys, derived from the rock beneath where it lies. In glaciated districts the material is commonly brought from a considerable distance, often from miles away.
THE VALLEY LOWLANDS. Were they planed by graded or ungraded streams? Have the present streams reached grade? Why did the streams cease widening the floors of the valley lowlands? How long since? When will they begin anew the work of lateral planation? What effect will this have on the ridges if the present cycle of erosion continues long uninterrupted?
The proportion of peculiar species, many of them of tertiary aspect, is confessedly large; and great aqueous erosion suffered by the white chalk, before the pisolitic limestone was formed, affords an additional indication of the two deposits being widely separated in time.
And, naturally, one is not to expect resolution in cases where there exist erosion and ossification of cartilage where crepitation is discernible. Paralysis of the Hind Leg. Aside from paraplegic conditions due to disease of the cord or the lumbosacral plexus, and monoplegic affections resultant from disturbances of this plexus, paralysis of certain nerves are occasionally encountered. Anatomy.
Michael's Mount represents that rock as having once stood in the centre of woodland. It is impossible to say when or how the Scillies first became insular, whether by sudden cataclysm or by gradual erosion; the latter seems more likely, but tradition has preferred to speak of a sudden catastrophe, such as that which is supposed to have overwhelmed Cardigan Bay.
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