Geoscience Reference
In-Depth Information
The present-day landscape that has been eroded in the Permian and younger sedi-
ments is generally flatter and lower than that of the older bedrocks, because the young-
er rocks are relatively weak in the face of stream erosion.
The Early Tertiary Petrockstowe Basin (
c3
), some 7 km south of Great Torrington,
formed along the Sticklepath Fault (Fig. 39) as a result of sinking movements asso-
ciated with fracturing and movement along the fault. Streams carried clays into this
basin, from which they have been extracted commercially, as with the Bovey Basin in
Area 2.
Along the north coast for several kilometres from Minehead, southeasterly to Blue
Anchor Bay, much of the actual coastline is backed by a flat platform with its upper
surface 5-8 m above sea level. Low water reveals a shore of boulder-strewn sand, ex-
cept in Minehead itself, where the Strand consists of relatively well-sorted sand. This
reflects the way that this northeast-facing part of the coast is sheltered from the storm
waves that sweep in from the west. Behind the platform, slopes rise abruptly to the
main inland hills, and a number of valley mouths and isolated hills were carved during
New Red Sandstone times, and perhaps as late as the early Jurassic. This ancient land-
scape has much more recently been filled with river sediments, which have then, in
turn, been covered by seashore deposits, probably reflecting an interglacial high-stand
of the sea. This interesting succession of sediments is now being overlain by younger
coastal deposits formed during the recent Flandrian (postglacial) rise of sea level.
Landscape D: Lundy Island
I have defined a separate Landscape for this island because it is so distinctive, not only
in form, but also in its location.
Lundy Island (Fig. 91) measures approximately 5 km north to south and only
about 1 km in width. The highest hill top is 142 m above sea level, but the island is gen-
erally flat-topped and surrounded by steep cliffs that provide homes to many seabirds.
The northern part of the island comprises desolate heathland, while the main settlement
is in the southern part, where the land is divided into small fields and pastures. Most
visitors are attracted to Lundy by a natural sense of curiosity, stimulated by its isolated
setting.
Most of the island is granite, the same type of igneous rock as many other areas in
the Southwest, but the Lundy granite was emplaced in the crust much more recently:
about 65 million years ago, compared with some 300 million years ago for the other
Southwest granites. The Lundy granite was intruded relatively recently into Devonian
sediments that had been deformed into slates during the Variscan mountain-building
episode, some of which can be seen in the southeast of the island, near to the landing
beach. The Lundy granite formed as the core of a volcano, being the southernmost vis-
