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Part of the action of the waves between high and low watermark must be included in subaerial denudation, more especially as the undermining of cliffs by the waves is facilitated by land-springs, and these often lead to the sliding down of great masses of land into the sea.
The white Chalk, when it was still in horizontal stratification, but after it had suffered considerable denudation, subsided gradually, so that the lower beds of drift Number 2, with their littoral shells, were superimposed on the Chalk in a shallow sea. Second. The overlying unstratified boulder clays 3 and 4 were thrown down in deeper water by the aid of floating ice coming from the north.
Suppose, therefore, we had ascertained that the triturating power of subaerial denudation might in a given time in three, or six, or a greater number of millions of years pulverise a volume of rock equal in dimensions to all the present land, we might yet find, could we revisit the earth at the end of such a period, that the continents occupied very much the same position which they held before; we should find the rivers employed in carrying down to the sea the very same mud, sand, and pebbles with which they had been charged in our own time, the superficial alluvial matter as well as a great thickness of sedimentary strata would inclose shells, all or a great part of which we should recognise as specifically identical with those already known to us as living.
The reason for this is that each person has a cultivated immunity to a given toxic state of the intestinal contents, and when from pressure or the irritation caused by a calculus. there is a denudation of the mucosa the infection that takes place has not the power to arouse a systemic resistance' but can cause only a local inflammation; this inflammation may end in ulceration, or it may cause a thickening of the parts and interfere with drainage from mucous or glandular pockets; then the locked up secretions become intensely toxic, and this sets up a new infection much greater then l the first and powerful enough to cause the system to call out its militia to put down the rebellion.
In the vast lakes which still remained on either side of the Rocky range, tertiary strata were slowly formed to the ultimate depth of two or three miles, enclosing here and there those vertebrate remains which were to be exposed again to view by denudation when the land rose still higher, and then, in our own time, to tell so wonderful a story to the paleontologist.
This mass has suffered much denudation; and the hard mica-schist has been deeply worn, since the period of its deposition; and this period must have been subsequent to the denudation of the basaltic lava-streams, as attested by their encircling cliffs standing at a higher level.
The physical possibilities were arrayed against the project, so steep was the comblike summit on either side, so heavy and tortuous the outcropping rock that served as the bony structure of the great mountain mass. True, the river pierced it, the denudation of solid sandstone cliffs, a thousand feet in height, betokening the untiring energy of the eroding currents of centuries agone.
As already remarked, no craters of eruption survive throughout the volcanic region of the North-east of Ireland, owing to the enormous extent of the denudation which this region has undergone since the Miocene Epoch; but the old "necks" of such craters in other words, the pipes filled with either solid basalt, or basalt and ashes are still to be found at intervals over the whole area.
But during the incalculable series of epochs thus implied, there existed an ocean, tides, winds, waves, rain, rivers. The agencies by which the denudation of continents and filling up of seas have all along been carried on, were as active then as now. Endless successions of strata must have been formed. And when we ask Where are they?
Matthew Herbert, and following them into the orchard, wandered about among the trees, under the curdled moonlight of the apple-blossoms, amid the challenges and responses of five or six nightingales, that sang as if their bodies had dwindled under the sublimating influences of music, until, with more than cherubic denudation, their sum of being was reduced to a soul and a throat.
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