Note: A downward flexure in the case of folded rocks makes a synclinal axis, and the alternating upward flexure an anticlinal axis.
The valleys within this range often follow anticlinal but rarely synclinal lines; that is, the strata on the two sides more often dip from the line of valley than towards it.
Owing to the amount of denudation which this chain has suffered, the outline of the gently inclined eastern flank scarcely offers the slightest indication of this synclinal axis.
Close to thesynclinal valley the dip of these strata is 45 degrees, but at the eastern or farther end of the series it increases to 60 degrees.
In the basin of the Lower Amazon the Carboniferous beds lie within the Devonian synclinal and crop out on both sides of the river next to the Devonian bands.
These bands are often concealed by more recent deposits, but it is clear that in this region the Devonian beds form a basin or synclinal with the Amazon for its axis.
The drainage of the belt as a whole is anticlinal to a marked degree, for the three main synclinal lines are lines of great elevation, and the anticlines are invariably valleys.
The initial tendency to synclinal ridges was obviated in places by the weakness of the rocks situated in the synclines, but even then the tendency to retain elevation is apt to cause low ridges.
Anticlinal and synclinal folds are symmetrical when the dip or slope of the strata is the same on both sides and the axial plane is vertical.
Besides the anticlinal and synclinal folds already explained, there are folds that slope in only one direction, one-sided or monoclinal folds (Fig.
It is very interesting to notice the relations of anticlinal andsynclinal folds to the agents of erosion.
When Sun-spots are at or near their maximum, the Corona has generally been somewhat symmetrical, with synclinal groups of rays making angles of 45° with its general axis.
The Cretaceous beds lie in a broad synclinal upon the eastern flank, but the greater part of the chain is formed of Jurassic beds, through which, on the western margin, rise the numerous andesitic volcanic centres.
Where they dip away from the axis of movement the structure is termed an anticline or anticlinal fold; where they dip towards the axis, it is a syncline or synclinal fold.
On the other hand, in advancing southwards along the synclinal axis, he loses stratum after stratum and gets into lower portions of the series.
Section of Anticlinal and Synclinal Folds on the line CD (fig.
The synclinal valleys of Bantry Bay and Dunmanus Bay were also, in all probability, submerged at this same early epoch.
Another synclinal of Carboniferous Limestone runs from Millstreet through Lismore, and the Blackwater has worn out an easy course along it.
The Lee, rising in the Old Red Sandstone moors of Gouganebarra, runs east, encountering one or two patches of limestone in the floor of the synclinal on its way, mere residues of the rock that once occupied the hollow.
Then the Old Red Sandstone again rises as an undulating upland through the centre of the county, with a few synclinal patches of Carboniferous Shale and Limestone caught in on its back.
The Blackwater, rising on Upper Carboniferous beds on the Kerry border, thus falls steeply southward to Rathmore, and then turns eastward along the synclinal valley of limestone from Millstreet to Cappoquin.
Near Cork, the limestone and accompanying shale are better preserved; but the river, instead of continuing along the synclinal through Middleton to Youghal, turns south, and forms the now submerged valley of Cork Harbour.
The present surface of anticlinal sandstone ridges and synclinal limestone hollows thus began to arise; but the main streams still held on their courses across the strike, that is, from north to south.
Besides the numerous minor flexures the schists are bent into a broad synclinal fold which crosses the county, its axis lying in a south-westerly-north-easterly direction.
The arches of the strata the geologist calls anticlines or anticlinal folds, and the troughs he calls synclines or synclinal folds (Fig.
Lines drawn along the summits of the ridges, A, B, would be anticlinal lines, and one following the bottom of the adjoining valleys a synclinal line.
Subsequent movements produced in the Nova Scotia and the adjoining New Brunswick coal-fields the usual anticlinal and synclinal flexures.
After passing this synclinal line the beds begin to dip in an opposite or north- easterly direction, acquiring a steep dip where they rest unconformably on the edges of the Upper Silurian strata of the Cobequid Hills, as shown in Figure 447.
And your experience indicates that this is more likely to happen at the first rise of the synclinal on a grade than anywhere on a straight track.
Superimposition of the Susquehanna on two synclinal ridges.
The present course of the middle Susquehanna leads it through the apical curves of two Pocono synclinal ridges, which were disregarded in the statement given above.
In the meantime, the former lake basin was fast becoming a synclinal mountain of diminishing perimeter.
The relief of the surface is moderate, except around the synclinal troughs, where the rising margins of the hard beds still appear as ridges of more or less prominence.
There is not a single case in the state of a stream cutting a gap at the apex of such a synclinal curve, but there are perhaps hundreds of cases where the streams notch the curve to one side of the apex.
The Delaware had little success, except as against certain eastern synclinalbranches of the Anthracite, for the same reason.
Thus we have the great Kittatinny or Cumberland highland, C, C, on the southeast, backed by the older mountains of Cambrian and Archean rocks, falling by the Kittatinny slope to the synclinal lowland troughs of the central district.
It is true that most of our streams now run out of and not into the synclinal basins, but a reason for this will be found later; for the present we look only at the location of the streams, not at their direction of flow.
In the majority of cases, an anticlinal axis forms a ridge, and a synclinal axis a valley, as in A, B, fig.
If depression take place along a given line, as at c, the strata will dip towards this line, and it will be a synclinal axis.
A synclinalaxis would also be produced by an elevation of the strata, as at d and e, on each side of it, and the valley thus produced is one of elevation.
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.
An anticlinal arrangement of strata is a weak structure--it readily succumbs to the attacks of the denuding agents; a synclinal arrangement on the contrary, is a strong structure, which is much less readily broken up.
If an anticlinal arch be a weak structure, a synclinal arrangement of strata is quite the opposite.
Several of the most marked hollows run along the backs of anticlinal axes, while some of the most conspicuous mountains are built up of synclinal or trough-shaped strata.
In the synclinal troughs, however, although much fissuring would take place, yet the strata would be compelled by the pressure to keep together.
Moreover, if it owed its existence to a great synclinal fold, why, he asks, does it not run along the same line as far as the same structure continues?
But in synclinal beds the action of these powerful agents is opposed by the structure of the rocks--and great rock-falls and landslips cannot take place.
The peninsula of Cornwall and Devon may be looked upon as formed from a synclinal trough of Devonian rocks, which appear as plateaus on the north and south, while the centre is occupied by Lower Carboniferous strata at a lower level.
The Coal Measures rest upon the Millstone Grits in most places, generally in synclinal basins.
The great coal-field on the south is a perfect example of a synclinal basin, the Millstone Grit and Carboniferous Limestone which underlie the Coal Measures appearing all round the margin.
The anticlinal ridges have thus been transformed into topographic valleys and the original synclinal troughs left in relief as plateaus and ridges.
Many such synclinal mountains or plateaus, separated by narrower anticlinal valleys, occur throughout the Appalachians.
This reversion of what would have been ridges and troughs had there been no erosion, is illustrated by the following cross-section through Lookout Mountain in Alabama, which is an example of what is known as a synclinal mountain.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "synclinal" in a variety of sentences. We hope that you will now be able to make sentences using this word.
