1911 Encyclopædia Britannica/Cheviot Hills

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15413221911 Encyclopædia Britannica, Volume 6 — Cheviot Hills

CHEVIOT HILLS, a range forming about 35 m. of the border between England and Scotland. The boundary generally follows the line of greatest elevation, but as the slope is more gradual southward and northward the larger part of the range is in Northumberland, England, and the lesser in Roxburghshire, Scotland. The axis runs from N.E. to S.W., with a northward tendency at the eastern end, where the ridge culminates in the Cheviot, 2676 ft. Its chief elevations from this point south-westward fall abruptly to 2034 ft. in Windygate Hill, and then more gradually to about 1600 ft. above the pass, followed by a high road from Redesdale. Beyond this are Carter Fell (1815) and Peel Fell (1964), after which two lines of lesser elevation branch westward and southward to enclose Liddesdale. The hills are finely grouped, of conical and high-arched forms, and generally grass-covered. Their flanks are scored with deep narrow glens in every direction, carrying the headwaters of the Till, Coquet and North Tyne on the south, and tributaries of the Tweed on the north. The range is famous for a valuable breed of sheep, which find abundant pasture on its smooth declivities. In earlier days it was the scene of many episodes of border warfare, and its name is inseparably associated with the ballad of Chevy Chase. The main route into Scotland from England lies along the low coastal belt east of the Till; the Till itself provided another, and Redesdale a third. There are numerous ruins of castles and “peel towers” or forts on the English side in this district.

Geology.—The rocks entering into the geological structure of the Cheviots belong to the Silurian, Old Red Sandstone and Carboniferous systems. The oldest strata, which are of Upper Silurian age, form inliers that have been exposed by the denudation of the younger palaeozoic rocks. One of these which occurs high up on the slopes of the Cheviots is drained by the Kale Water and the river Coquet and is covered towards the north by the Old Red Sandstone volcanic series and on the south by Carboniferous strata. Another area is traversed by the Jed Water and the Edgerston Burn and is surrounded by rocks of Old Red Sandstone age. The strata consist of greywackes, flags and shales with seams and zones of graptolite shale which yield fossils sparingly.

On the upturned and denuded edges of the Silurian strata a great pile of contemporaneous volcanic rocks of Lower Old Red Sandstone age rests unconformably, which consists chiefly of lavas with thin partings of tuff. A striking feature is the absence of coarse sediments, thus indicating prolonged volcanic activity. They cover an area of about 230 sq. m. in the eastern part of the Cheviots and rise to a height of 2676 ft. above the sea. The lavas comprise dark pitchstone, resembling that at Kirk Yetholm, and porphyritic and amygdaloidal andesites and basalts. This volcanic platform is pierced by a mass of granite about 20 sq. m. in extent, which forms the highest peak in the Cheviot range. It has been described by Dr Teall as an augite-biotite-granite having strong affinities with the augite-bearing granitites of Laveline and Oberbrück in the Vosges. Both the granite and the surrounding lavas are traversed by dykes and sills of intermediate and acid types represented by mica-porphyrites and quartz-felsites.

On their north-west margin the Lower Old Red volcanic rocks are covered unconformably by the upper division of that system composed of red sandstones and conglomerates, which, when followed westwards, rest directly on the Silurian platform. Towards the south and east the volcanic pile is overlaid by Carboniferous strata, thus indicating a prolonged interval of denudation.

On the northern slopes of the western part of the Cheviots the representatives of the Cementstone group of the Carboniferous system come to the surface, where they consist of shales, clays, mudstones, sandstones with cementstones and occasional bands of marine limestone. These are followed in normal order by the Fell Sandstone group, comprising a succession of sandstones with intercalations of red and green clays and impure cementstone bands. They form the higher part of the Larriston Fells and are traceable eastwards to Peel Fell, where there is evidence of successive land surfaces in the form of dirt beds. They are succeeded by the Lewisburn coal-bearing group, which represents the Scremerston coals.