North Cornwall Research Articles

Quartz-Carbonate Veining and Deformation in Namurian Turbidite Sandstones of the Crackington Measures, North Cornwall

Turbidite sandstones interbedded with argillites are cut by veins composed of quartz and ankerite derived from host sandstones during successive phases of deformation.The existence of the oldest phase of deformation (F1) is established by the presence of its widespread vein system, which is folded by the F2 folds and cut by quartz veins of the later deformation phases.The nature of the veining, its mode of origin and regional significance are considered.

Repeated folding at Boscastle, North Cornwall, England

Repeated folding of the Boscastle Measures, a group of thinly bedded sandstones and shales of presumed Upper Carboniferous age, has led to the development of small-scale superimposed structures. The earliest folds are now isoclinal with a strongly developed axial-plane slaty cleavage and a prominent mineral elongation parallel to fold axes. Although the regional trend of the southern margin of the Culm Measures trough of north Cornwall and mid-Devon is east to west, the early folds at Boscastle are recumbent with predominantly a gentle plunge to the north. Of lesser importance is the more nearly east to west trend of some isoclines. It is suggested that the two trends of isoclines may be linked in synchronous right-angled combinations, and that this pattern may be reflected on a large scale in the outcrops south of Boscastle. The isoclines are deformed by small-scale east to west zigzags, believed to be related to northwards movements down major low-angle normal faults which are parallel to the gently inclined bedding.

Action of urea on calf-thymus deoxyribonucleic acid

Despite representing a key parameter when modelling morphology or sediment transport, surface sediments are often assumed homogenous, with grain size temporally constant. This contribution uses a 6-year data set of monthly sediment samples to quantify the observed variability in intertidal beach sands at four energetic, macrotidal locations (North Cornwall, UK). Changes in grain size and sorting were related to periods of high-steepness storm waves promoting a relatively rapid coarsening and an improvement in sorting and low-steepness swell waves, a fining and a reduction in sorting. These temporal changes in intertidal grain size were coherently linked to the disequilibrium in wave steepness, with peak coarsening occurring when the instantaneous wave steepness conditions vastly exceeded a temporally evolving antecedent time series. Using this concept, a simple model is proposed that provides skilful predictions of the unseen variability in sediment grain size (average r2 = 0.86, p < 0.01) and sorting (average r2 = 0.75, p < 0.05), at all four sites.

Directional recording of swell from distant storms

Almost fifteen years ago in the pages of this Journal, one of us presented power spectra of ocean waves and swell off Pendeen and Perranporth in north Cornwall (Barber &amp; Ursell 1948). The outstanding feature of these spectra is the successive shift of peaks toward higher frequencies. This is the expected behaviour of dispersive wave trains from rather well-defined sources. Storms generate a broad spectrum of frequencies; the low frequencies are associated with the largest group velocity and accordingly are the first to arrive at distant stations. The time rate of increase in the frequency of peaks determines the distance and time of origin. In this way Barber &amp; Ursell were able to identify the dispersive arrivals with a low pressure area in the North Atlantic, a tropical storm off Florida, and a storm off Cape Horn, at distances of 1200, 2800, and 6000 miles, respectively, from the Cornish stations. The measurements were consistent with the simple classical result that each frequency,/, is propagated with its appropriate group velocity, V = g/(47[/*). The present study is in a sense a refinement to the work of Barber &amp; Ursell. The frequency resolution and sensitivity have each been increased by an order of m agnitude, and this makes it possible to detect and resolve meteorological sources that have previously been out of reach. The antipodal swell from the Indian Ocean is a case in point

Discussion

Dr J. M. H ancock asked the author how many specimens had he had available. Only one ammonoid from the Lower Devonian had been mentioned, although clearly most of the author's divisions were true faunizones. Second, were the ammonoids spread evenly through the succession or concentrated in particular beds? What hints would he offer to anyone going to collect for himself? Third, would he care to comment on the distribution of the ammonoids among the different facies he had mentioned ? Mr S. C. M atthews commented on the author's suggestion that it was possible to recognize in south Devon and north Cornwall a more northerly, ammonoidrich Upper Devonian facies-belt flanked on the south by slate occurrences of the same age. The suggestion received some support from work in progress in the Tamar Valley, where a well-exposed Upper Devonian slate succession appeared to lack ammonoids and was therefore to be contrasted with Selwood's Launceston succession immediately to the north. It seemed likely, however, that Dr House and the speaker would agree in suspecting that further work would reveal a more complex distribution of fades than was suggested in Dr House's present tentative recognition of two major belts. The speaker welcomed proof of Middle Devonian age for a part of the Padstow succession that had yielded styliolinids. An isolated mass of limestone in the Tamar Valley was thought to be of Upper Devonian age by Ussher, who found Styliolina there; but the limestone had now yielded a conodont fauna that provided clear evidence

Some Observations on Slope Development in North Devon and North Cornwall

Some Observations on Slope Development in North Devon and North Cornwall

The Structure of Mid-Devon and North Cornwall

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Studies on the biology of limpets IV. The breeding of patella depress a pennant on the north Cornish coast

SUMMARYThe breeding of Patella depressa was studied at Trevone, North Cornwall, for 4 years. Gonads were examined and assessed by methods described in a previous report on P. vulgata.In contrast to the common Limpet, P. depressa is a summer breeder in Cornwall. Gonad development begins in the spring and is complete by June or July. Spawning coincides with maximum air temperatures in July, August or early September. The autumn and winter period is passed with gonads in recognizable post-spawning and spent stages, and only a small proportion of completely resting neuter gonads is found in the early spring.Mass spawning takes place, and gametes are voided rapidly. No definite spawning stimulus can be shown, but, as with P. vulgata, there may be some relation between onset of spawning and the occurrence of wave action on the shore.The differences in breeding behaviour of P. depressa and P. vulgata reinforce the other differences between them and throw some doubt on the concept of super-species in Patella.

Spilitic Rocks in South-east Devonshire

AbstractVolcanism began in South-east Devonshire with the extrusion of keratophyric tuffs in the Lower Devonian. The majority of extra ves in the Middle and Upper Devonian are basic spilites but there are intermediate varieties. Volcanism in the Middle Devonian was local and in the Ashprington area appears to have been continuous throughout the epoch. At the beginning of the Upper Devonian keratophyric crystal and vitric tuffs were extruded in the Dartington area. Later in the Upper Devonian the Chipley pillow lavas were extruded: it is shown that these lavas were widespread and may probably be correlated with similar lavas at Pentire Head in North Cornwall. The final phase of volcanism is represented by the intrusion of swarms of sill-like bodies of spilitic dolerites in Upper Carboniferous times. Intrusive and extrusive rocks are distinguished, mapped, and classified petrographically

WEST COUNTRY SHIPYARD PRACTICE IN THE DAYS OF WOODEN SHIPS

Vernon Boyle is known to members of the Society for Nautical Research for his masterly article ‘The Bideford Polackers’ (M.M., Vol. XVIII (1932), pp. 109–24), published in the early days of a welcome revival of interest in regional craft. He also wrote the North Devon part of Devon Harbours (London: Christopher Johnson, 1952), and contributed a number of papers to learned societies in his native county, of which probably the most notable was ‘Arts and Crafts of an Old Seaport’ (Trans. Devonshire Association…, Vol. LXXX (1948), pp. 137–45). All were beautifully illustrated with line drawings, for he was a renowned artist in that and other media, and the text had an easy, readable style, none the less as complete and detailed as one would wish. Boyle collected material of North Devon and North Cornwall interest, architectural as well as nautical, and at the time of his rather sudden death in June 1954, had for two or three years been preparing some of his sea lore for a book which was to appear in our joint...

Discovery of Ammonoids of the Upper Devonian Wocklumeria Zone in North Cornwall

RECENTLY, Dr. R. Goldring1 has been able to make a direct correlation of the lower part of the Pilton Beds of North Devon with the Wocklumeria Zone of the Sauerland, Germany. This correlation is based on the trilobites which occur both with the brachiopod faunas of the Pilton Beds and the ammonoid faunas of the Sauerland. Thus the German faunal horizon was precisely identified in England for the first time.

Devonian Goniatites from North Cornwall

AbstractA study of Devonian faunas from North Cornwall shows that a considerable area of beds hitherto regarded as Upper Devonian are of Middle Devonian age. Goniatite localities at Trevone Bay and Portquin correlate with the Upper Maenioceras Stufe of Germany: other localities within the area mapped as Grey Slate by the Survey are also Middle Devonian. Only the area marked as Purple and Green Slate by the Survey has yielded Upper Devonian goniatites.

Studies on the biology of limpets: II. The breeding of Patella vulgata L. in Britain

Some preliminary observations in North Cornwall (Orton, 1946) showed that the periods of breeding of the three British species of limpets were different. In order to determine these differences more accurately, and to study the breeding cycle, samples of limpets from six localities in Britain were examined at regular intervals for 5 years. This paper gives the results obtained for the common limpet Patella vulgata, which was present at all the localities sampled and was the most intensively studied of the three species. Later papers will deal with the remaining species and with other aspects of the investigations.

An Excavation at St. Mawgan-in-Pyder, North Cornwall

An Excavation at St. Mawgan-in-Pyder, North Cornwall

The influence of rock structures on coast-line and cliff development around Tintagel, North Cornwall

The paper deals with the morphology of the stretch of coast between Boscastle and the Treligga Cliffs in North Cornwall. The prevalent cliff type is slope-over-wall, either hog's-back or bevelled as defined by Miss Arber (1949). Flat-topped cliffs are less common. It is considered that geological structures—bedding, jointing, faulting and, to a lesser extent, rock-type—have not only had considerable influence on the shape of the cliffs, but have also guided the marine attack on the coast. The evolution of most of the coast features, when seen in plan or profile, has been controlled by the local geological structure. The southern stretch of the coast is sub-parallel to seaward-dipping normal faults which have been stripped of their hanging-walls. Such a cliff line is dominantly a faultline scarp which has suffered slight retrogression.

The tectonics of the Tintagel area, North Cornwall

Summary The paper describes the structure of the coastal region of North Cornwall in the neighbourhood of Boscastle, Tintagel and Trebarwith Strand. The area has been remapped, and the tectonics originally outlined by Dewey (1909) have been reinterpreted. The revision has shown that the epidiorite at Tintagel is more extensive than hitherto believed. Massive epidiorite grades into chlorite-schist which is often very similar in appearance to the sheared volcanic rocks of the area; but the schist derived from the intrusive rock can be identified by its local thermal metamorphism of the phyllites which lie above it. The important tectonic episode in the area was that of thrusting, in which the upper beds moved from the south-south-east towards the north-north-west. The direction and sense of the translation is indicated by various minor structures, e.g. slickenside striations, elongations of lava pillows, amygdules etc., in a (the movement direction); and by drag-folds, zig-zag folds, boudinage structure, tension fractures etc. in b (normal to a ). Three main thrust-zones are recognized, and they separate the rocks into three tectonic units or thrust-slices which lie on an autochtonous foundation. The higher thrust-slices lie to the west of the lower ones because they have been preserved from erosion by the local westerly dip aided by normal faulting which downthrows to the west-north-west. The more important of these normal faults pass through Tintagel Haven and form, inter alia , the great fault complex seen in the cliffs of the Island. Similar faulting occurs at Trebarwith Strand, Lill Cove and Hole Beach. In each case the downthrow is such that the flat thrust-plane there is dropped to the west. The general direction of strike in the area is controlled by the gentle doming due to the Davidstow Anticline. This hemidome pitches north-westerly, and it developed later than the thrusting episode. The evidence shows that there is no connexion between the thrust movements which carried the beds forward at least 2½ miles (or more) and the warping of the anticline. The tectonics at Tintagel are thus no longer to be considered the result of thrusting from the west-north-west, but are rather the result of a major movement from the south-south-east, and so become an integral part of the Hercynian tectonic pattern of Cornwall.

Cliff Profiles of Devon and Cornwall

The coast scenery of North Devon and of North and West Cornwall con? sists mainly of rugged cliffs, ranging in profile from the hog's-back slopes around Lynmouth to the sheer precipices of Morwenstow. The loftiest hog'sback cliffs (Plate i) are those in north-east Devon between Combe Martin and Foreland Point, extending still farther east across the Somerset border. The Great Hangman near Combe Martin has a crest 1044 feet above sealevel about 300 yards inland, whence a straight vegetated slope of gradient approaching 1 in 1 descends to the very base, which alone is now subject to wave attack. The clifTs between Hartland Point and Widemouth afford a complete contrast. An inland plateau sloping gently towards the sea is cut clean by an almost vertical cliff face, 400 feet high near Morwenstow and nearly 300 feet high at Hartland Quay (Plate 2). Where the profile, as at the Lizard and the Land's End, does not conform to either of these two extremes, a vegetated slope curves in a bevel from the level surface above to the vertical cliff face below. The curve may be concave (Plate 3) or convex (Plate 4). The greater part of the area considered in this paper (see map) consists of Devonian and Carboniferous rocks. Along the coast the commonest of these are hard grits, shales, sandstones and slates; there are also small outcrops of Devonian igneous rocks. At the end of the Carboniferous period the region was evidently subjected to severe pressure along Armorican lines, resulting in a series of folds with east and west strike. The north of the area is occupied by a great synclinorium, so that in North Devon the regional dip is to the south while along the coast, roughly from Boscastle to Morwenstow, it is to the north. During the same orogeny the great granite domes of Devon and Cornwall were intruded, which outcrop on the mainland coast at the Land's End.

Food-vessel and Flint Spear-head, Pentire Glaze, Polzeath, North Cornwall

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The Vegetation of the Sand Dunes of the Camel Estuary, North Cornwall

A considerable number of papers have already appeared, describing the vegetation occurring on sand dunes in the British Isles, and the pioneer stages in the colonization of mobile dunes seem to conform generally to a well-marked type. When, however, the sand has become partially fixed, a large number of non-maritime species are able to gain a foothold, and in this stage the composition of the vegetation as it passes into 'fixed dune' shows a great variety in the areas which have been studied. The species occurring must clearly depend to a large extent on the proximity of seed parents and also on the power of a particular species to survive in sand which is still partially mobile. The ultimate vegetation must also be influenced by the nature of the sand. The front dunes in all areas which have been studied seem to be generally alkaline, largely as a result of their salt content. Where the sand contains little CaCO3, however, the older dunes tend to become acid and the subsequent vegetation is accordingly influenced. The chief interest in the present study lies in the fact that the sand, even in the oldest and most fixed portions of the area, is always highly calcareous and contains at least 50% CaCO3, with a pH exceeding 8-0. The other feature of interest about these Cornish dunes is that they include a well-defined area of dunes which have recently been formed and whose age is known with some accuracy. These dunes show the early stages of colonization very clearly. It will be seen from the lists of species included in this paper that this area is no exception in supporting a very varied flora, including some species which do not seem to have been recorded from similar habitats elsewhere. An analysis of the vegetation occurring on more or less fixed dunes in a number of localities in the British Isles and Ireland has been included at the end of this paper. This list, besides showing something of the great variety of the flora, shows that a number of non-maritime species occur in this type of habitat with considerable regularity. It had been hoped to include in this paper studies of the more extensive sand-dune areas along the north Cornish coast, at Perranporth and elsewhere, but transport difficulties have unfortunately made this impossible. The area studied is situated on the east side of the Camel estuary on the coast of north Cornwall, opposite the little port of Padstow (see Fig. 1). The front of the dunes extends from a point just south of Brea Hill to the village of Rock, a distance of about 2Ikm. Behind this is a large area of fixed dune and blown sand, which extends in some places for a distance of over I km. from the water's edge and reaches as far north as Daymer Bay. The blown sand covers, usually thickly, an area of slate or diabase, and much of it lies over 30 m. above the sea. The vegetation of the whole blown-sand area is very similar to that on the lower lying fixed dunes nearer the sea, which were more intensively studied for the detailed lists in this paper. Much of the blown-sand area is occupied by the St Enodoc Golf Course, with the result that the vegetation on the fairways and greens has been considerably modified.

A Study of the Vegetation of Sea-Cliffs in North Cornwall

It is well known that cliffs, which are above the reach of high tides, but exposed constantly to sea spray, support a characteristic vegetation of halophytes, most of which are also typical plants of salt-marshes. The composition of the cliff vegetation varies, however, a good deal in different districts of the British Isles and has not often been described in much detail. The present study has been undertaken with a view to gaining some information about the vegetation of 'spraywashed cliffs' in a part of the British Isles where non-halophytic species, such as the A,rt Ijac. arctic-alpines found on the north-west cliffs of Scotland and elsewhere, seem to be mostly absent, and the vegetation can be looked upon as reasonably typical. A kzonhu The area which was selected for study is situated about half-way down the north Cornwall coast and consists of the strip of coast-line starting at Trebetherick Point, on the east side of the Camel estuary near Polzeath, round Pentire and Rumps Points, m)sane f and then eastwards as far as Kellan Head (see Fig. 1). The length of this coast-line is | vi? t approximately 8 miles (13 km.), Less detailed observations have also been made at various Je eIr ck RLnl points on the west side of the Camel estuary as far west as Bedruthan Steps, and also RV> Cal. some miles eastwards in the neighbourhood of Tintagel. These more distant observations E have not revealed any new features in the Nr < general vegetation, and confirm the presumption that the area studied is typical of S&.le (Ato lmtile a long strip of coast. One of the advantages of the portion of coast chosen is that it is Fig. 1. very much indented and actually furnishes examples of all aspects between south-west and south-east, though the general aspect is north. The cliffs are mostly composed of Upper Devonian Slate, often showing purple or green bands. There are, however, various igneous intrusions of Diabase or of Pillow lava (Greenstone). The Pillow lava occurs principally round the Pentire peninsula, but Rumps