The Triassic deposits of the Atlantic Coast are much broken up into large fault blocks, and this faulting probably took place as a result of the crustal disturbances toward the end of the period.
For these reasons the surface and near-surface crustal portions are called the "zone of fracture," while the more deeply buried portions comprise the "zone of flowage.
The land on the east side of the fault moved south and that on the west side moved north, the amount diminishing away from the fault on each side so that some miles out the actual crustal movement was only a few inches.
Profound crustaldisturbances marked the close of the Jurassic period in the western part of the continent.
In general we may recognize two types of crustal movements--slow and sudden.
Certain crustal movements which have occurred about the Bay of Naples are of very special interest because actual human history dates can be placed upon them.
The close of the Cretaceous period, or what is the same, the close of the Mesozoic era, was marked by some of the grandest crustal disturbances in the known history of the earth.
Another type of crustal disturbance causes more or less profound changes in the structures of the rocks themselves.
Certain profound crustal disturbances marked the close of the period in western Europe, resulting in upturning and folding of rocks during the process of mountain forming from Ireland to Germany, and from Bohemia to southern France.
For yet another period of great volcanic activity ensued, connected, perhaps, with the crustal disturbances to which the origin of the Himalaya is attributed.
If they be relatively both high and narrow, the deformation is considerable, a larger amount of crustalshortening has gone on, and the folds are described as close (Fig.
Such chains are almost invariably composed of folded rocks, thus indicating that erosion has removed great superincumbent masses of strata since the crustalcompression produced the folds at considerable depths below the then surface.
As to the sun, there has hitherto been no conclusive evidence that it is related to crustal movements, although various writers have made suggestions along this line.
For example, the profound crustal changes at the end of the Mesozoic were not accompanied by widespread glaciation so far as is yet known, although the temperature appears to have been lowered.
From this has arisen the doctrine of isostasy, or of the equalization of crustal pressure.
Nevertheless climatic changes might occasionally set the date when the gravitative pull would finally overcome inertia, and thus usher in the crustal movements that close old geologic periods and inaugurate new ones.
Most important of all, a satisfactory explanation of climatic changes and crustal deformation must take account of all the agencies which are now causing similar phenomena.
Thus the erosion and deposition due to climatic variations presumably play their part in crustal deformation chiefly by producing crustal stresses, while the storms, as it were, strike sharp, sudden blows.
This might set up a state of strain which would ultimately have to be relieved, thus perhaps initiating profound crustal movements.
If heavenly bodies should approach the earth closely enough so that their gravitational stresses caused crustal deformation, all life would presumably be destroyed.
If this happened, mountains would be rare or unknown, and hence climatic contrasts would be far less marked than is actually the case on our earth where crustal movements have repeatedly been rapid enough to produce mountains.
Let us first inquire whether earthquakes, which are one of the chief evidences that crustal movements are actually taking place in our own times, show any connection with sunspots.
It is not too much to say that the character and thickness of each formation of the stratified rocks depend primarily on these crustal movements.
Thus, even at the beginning of the Paleozoic, the continental plateau of North America had already been left by crustal movements in relief above the abysses of the great oceans on either side.
This rock may be made by the consolidation of volcanic cinders, of angular waste at the foot of cliffs, or of fragments of coral torn by the waves from coral reefs, as well as of strata crushed by crustal movements.
Why crustal movements occur is not definitely known though many theories have been advanced to explain them.
Beautiful Zion Canyon, therefore, has been created as the result of crustal movements bringing into action the effective cutting power of running water, assisted by all the ever-working forces of disintegration and decay.
Everywhere are found the evidences of those great processes of nature—erosion of the high country, land formation in the low country, and mighty crustal movements slowly raising or lowering the land in both.
It was relatively late in the last chapter of the earth’s history (Cenozoic Era) that the cutting of Zion and associated canyons was made possible by gradual though tremendous crustalmovements in the region.
Built up originally as great horizontal deposits of sand and mud, they were bent by mighty crustal movements until high mountains, probably comparable to the present Alps, were formed.
The bold forms of the St. Elias Alps, also described by Russell, are regarded by him as chiefly produced by the tilting of huge crustal blocks on which erosion has as yet done relatively little work.
The increasing volume of shallow-water sediments of uniform character near the end of the Silurian, indicates great crustal stability at a level which brought about neither a marked gain nor loss of material to the region.
Though their deformed condition indicates a period ofcrustal disturbance, the Tertiary beds give no indication of wholesale transformations.
Considerable crustal movements affected the American coast-lines in Mesozoic times, and during these uplifts the strata suffered fracture and displacement, but were subjected to comparatively little folding.
From this point of view it is the lithosphere that is unstable, all changes in the relative level of land and sea being due to crustal movements.
Since the close of that period many crustal oscillations have taken place, but no grand mountain-ranges have again been ridged up on the Atlantic sea-board.
Perhaps the latter is the more probable supposition, for it seems very unlikely that crustal disturbances, resulting in axial and regional uplifts, should have been confined to the continental plateau only.
It would seem most likely, in short, that the volcanic action in question was connected mainly with crustal movements in the oceanic trough.
Two kinds of crustal movement, as we have seen, are recognised by geologists.
The other kind of crustal disturbance takes place more markedly in linear directions, and is always accompanied by abrupt folding and mashing together of strata, along with more or less fracturing and displacement.
To sum up, then, we may say that the chief agents concerned in the development of coast-lines are crustal movements, sedimentation, and marine erosion.
As time went on land continued to be developed along the same lines, a result due partly to crustal movements, partly to sedimentation.
It resembles the latter also in the greatness and irregularity of its depths, and in the evidence which its islands supply of volcanic action as well as of very considerable crustal movements within recent geological times.
Should they preserve that position, undisturbed by crustal oscillation, for a prolonged period of time, they will eventually be cut back by the sea.
Like its European parallel, it has been diminished by sedimentation and crustal movements.
But notwithstanding all the evidence of recent extensive crustal movements in this region, it is obvious that the Mexican-Caribbean depression, however much it may have been subsequently modified, is of primitive origin.
Or again, they may arise in crustal disturbance of a volcanic nature, primarily induced or localised by the crossing of two canals.
Such lines mark out the theoretical axes of the "double canals" which futurecrustal movements will more fully develop.
The fact of radioactive heating allows us to assume the thin surface crust and continued sub-crustal energy throughout the entire period of the planet's history.
We have referred to these well-known episodes with two objects in view: to recall to mind the time-interval involved, and the evidence of intense crustal disturbance, both dynamic and thermal.
The lines most conspicuous in the telescope are, in short, those which have been favoured by a combination of circumstances as reviewed above, among which crustal features have, in some cases, played a part.
It is therefore believed by many geologists that it is pressure due to crustal movements and internal stresses which squeezes molten rock from below into fissures and ducts in the crust.
In intimate relationship with the mountain-building orogenic crustal movements was the prevalence of volcanic activity during the earlier part of this period.
In a typical "island-arc" environment, volcanoes lie along the crest of an arcuate, crustal ridge bounded on its convex side by a deep oceanic trench.
Because the granitic crustal layer is absent, the magmas are not appreciably modified or changed in composition and they erupt on the surface to form basaltic volcanoes.
Ewing and Ewing (in press) suggest that this intermediate velocity is the result of a physical mixture of oceanic crustal rocks and mantle rocks.
The rough fields over the oceanic rises and ridges were attributed to variations in the susceptibility of the crustal rocks, probably related to volcanic extrusions and intrusions.
The topographic change from abyssal floor to the Bermuda Rise is accompanied by a corresponding change in crustal structure (Fig.
On the basis of the observed correspondence of crustal structure and physiographic provinces a hypothetical trans-Atlantic structure section was prepared (Fig.
Seismic-refraction studies of the Pacific Ocean basin, Part I, Crustal thickness of the equatorial Pacific: Geol.
The crustal structure of the Mid-Atlantic Ridge provinces has been determined at about 20 places by the seismic-refraction technique (Fig.
The crustal structure of oceanic rises differs significantly from the typical abyssal floor in having lower velocities and generally thicker crustal layers.
These cannot be Pleistocene eustatic levels unless we consider that they were formed prior to recent large crustal deformations.
Ewing (in press), have shown that the average crustal structure of the crest provinces and Upper Step consists of 0.
The distribution of fossils frequently makes it possible to map out approximately the general features of land and sea in long-past geological periods, and so to enable the history of crustal relief to be traced.
The fundamental conception of geography is form, including the figure of the earth and the varieties of crustal relief.
Lapworth has generalized the grand features of crustal relief in a scheme of attractive simplicity.
The dominant forms result from crustal movements, the subsidiary from secondary reactions during the action of the primitive forms on mobile distributions.
Geologists would report on the crustal relief (as the features of Mother-Earth are inelegantly termed).
He does not allow the "crustal relief" to have the upper hand in the matter.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "crustal" in a variety of sentences. We hope that you will now be able to make sentences using this word.
