We are told "the present rate of denudation of a continent is known with considerable accuracy from careful measurements of the quantity of solid matter carried down by rivers.
We have to fall back, therefore, on the geological evidence of deposition anddenudation .
Furthermore, whilst denudation is going on, a longer or shorter period of time elapses, during which the upheaved area receives no deposit, and accordingly no organisms which lived during that period are preserved in the upheaved area.
Indeed, some deep boring in the vicinity may prove that the ledges rest upon other layers of rock which extend downward for many hundreds of feet below the valley floor.
Taking this as the average rate of denudation for the land surfaces of the globe, estimates have been made of the length of time required at this rate to wash and wear the continents to the level of the sea.
It is they which uplift and recreate the lands which the agents of denudationare continually destroying; it is they which deepen the ocean bed and thus withdraw its waters from the shores.
The same lesson is taught as plainly by the amount of denudation which the lands suffered during the era.
Intrusive sheets are usually harder than the strata in which they lie and are therefore often left in relief after long denudation of the region (Fig.
What remains of these rock systems after the denudation of all later geologic ages is enormous.
As deposition in the sea corresponds to denudation on the land, we are able to make a general estimate of the rate at which the former process is going on.
The texture of the rock of bosses proves that consolidation proceeded slowly and at great depths, and it is only because of vast denudation that they are now exposed to view.
Layers of solid rock several miles in thickness have been crumpled and folded like soft wax in the hand, and a vast denudation has worn away the upper portions of the folds, in part represented in our section by dotted lines.
Either, then, the earth is very young and the agents of denudation have not yet had time to do their work, or they have been opposed successfully by other forces.
Before we consider how the waste of the land brought in by streams is rebuilt upon the ocean floor, we must proceed to study the work of two agents, glacier ice and the wind, which cooperate with rivers in the denudation of the land.
Under long denudation mountains are subdued to the forms characteristic of old age.
Assuming that the folded strata rested on an unyielding foundation, and that what was lost in width was gained in height, what elevation would the range have reached had not denudation worn it as it rose?
Thus denudation is most energetic on the southern slopes.
The river having been closed with ice within the last two days, we crossed it this afternoon to visit the two pyramidal monuments of geological denudation which mark the limestone range of the opposite shore.
Such rapid changes from complete saturation to sudden heat are trying to the hardest rocks, and at Hardraw, close at hand, there is a still more palpable process of denudationin active operation.
This denudation has had an undoubted effect upon the rainfall, and has served to change the climatic conditions in these regions.
If such existed, they may possibly be covered up in some places by more modern deposits, or may have been swept away by denudation in the intervening ages; but even in these cases we should expect to find some visible remains of them.
Hence over large spaces the Primordial is absent, being probably buried up, except where exposed by denudation at the margin of the two formations.
In the case of the great faults the upheaval along a given line would itself facilitate the denudation (whether subaerial or marine) of the upheaved portion at a rate perhaps a hundred times faster than plains and plateaux.
There is an enormous difference between mean and maximum denudation and deposition.
Oscillations in the Level of the Alps and lower Country required to explain the Formation and Denudation of the Loess.
After this subsidence, the re-elevation and partial denudation of the Cretaceous and glacial beds took place during a general upward movement, like that now experienced in parts of Sweden and Norway.
They afford evidence at many points of repeated denudation and redeposition, and may be the monuments of a long series of ages.
However, it resists denudation in a remarkable manner, and in China it often stands up in vertical walls hundreds of feet in height.
These changes were accompanied by some denudation followed by a grand submergence of several hundred feet, probably brought about slowly, and when floating ice aided in transporting erratic blocks from great distances.
It will be observed that the gravel Number 4 is obliquely stratified, and that its surface had undergone denudation before the white sandy loam Number 3 was superimposed.
Fissures filled in this manner from below, as denudation progresses, become exposed at the surface and reconcentration through the influence of disintegration and decay, and of solution and redeposition by descending water takes place.
For example, concentration through the action of mechanical agencies is illustrated by the manner in which rocks are reduced to fragments in the every-day process of denudation and the resulting debris removed by streams and redeposited.
Whenever land exists or the waves and currents of the ocean come in contact with the rocks denudation occurs.
How is the waste of land by denudation compensated?
And, second, we must not forget the intense denudation which they have experienced, so that miles and miles of strata which once existed have been swept away, and their materials built up into new formations.
What have been the general effects produced by denudation on the face of the land?
The first question implies the denudation of the valley below the level of the gravel, or the elevation of the whole plateau.
Only thus can we gain time at all sufficient to explain the truly astonishing amount of denudation which these great, though comparatively with most other ranges recent, mountains have suffered.
Sometimes the gravels in which such implements were originally deposited have disappeared through denudation or other natural causes, leaving the implements on the surface.
The particular bed marked EF has been entirely removed bydenudation from the top of the anticline, and is buried deep beneath the centre of the syncline.
The portion of an anticline which has been removed by denudation is the "aerial arch," dotted in fig.
For example, in many coal regions the deposits have been conserved in some districts in the synclines or "basins," while they have been removed by denudation from the uplifted anticlines in others.
By them, undoubtedly, was made the first breach over its top, thus commencing that slow but sure denudation which finally reached the rock below.
In other words, thousands of feet of strata have been removed by denudation from the high sides of faults.
But while the effects produced by the erosion of horizontal strata are readily perceived by the least-informed observer, it requires some knowledge of geological structure to appreciate the denudation of curved or undulating strata.
Hence it is that in all regions which have been exposed for prolonged periods to sub-aerial denudation synclinal strata naturally come to form hills, and anticlinal strata valleys or low grounds.
When, therefore, we encounter at the actual surface of the earth great mountain-masses of granite, we know that in such regions enormous denudation has taken place.
Another suggestion is that much of the material of the loess may have been derived from the denudation of the boulder-clays by flood-water, during the closing stages of the last cold period.
In later Palaeozoic times land began to extend in the Spanish peninsula, northern France, and middle Europe, the denudation of which doubtless furnished materials for the elaboration of the contemporaneous strata of those regions.
The latter are incomparably older than the former--the heights of the Atlantic borders being mountains of denudation of vast geological antiquity, while the coastal ranges of the Pacific slope are creations but of yesterday as it were.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "denudation" in a variety of sentences. We hope that you will now be able to make sentences using this word.
