Difference between revisions of "Easter excursions, North Cornwall, April 9th to 18th, 1914 - Geologists' Association excursion"
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(→Easter excursions, North Cornwall, April 9th to 18th, 1914 - (transcribed from: GA Circular No. 165. Session 1913–1914 p. 3–8)
(→Easter excursions, North Cornwall, April 9th to 18th, 1914 - (transcribed from: GA Circular No. 165. Session 1913–1914 p. 3–8))
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| | VI. Variegated slates (Famennian).
| | VI. Variegated slates (Famennian).
Revision as of 11:13, 20 October 2020
Easter excursions, North Cornwall, April 9th to 18th, 1914 - Geologists' Association excursion
- 1 Geologists' Association Circular No. 165. Session 1913–1914 p. 3–8
- 2 Easter excursions, North Cornwall, April 9th to 18th, 1914 - (transcribed from: GA Circular No. 165. Session 1913–1914 p. 3–8)
- 3 Good Friday, April 10th. Upper Devonian sequence and overthrusts
- 4 Saturday, April 11th. Upper Devonian sequence and overthrusts.
- 5 Sunday. No Official Programme.
- 6 Monday, April 13th. Upper Devonian beds of southern area, pillow lava and associated rocks
- 7 Tuesday, April 14th. Relations of Upper Devonian to Carboniferous Rocks: Pliocene features, and physiography
- 8 Wednesday, April 15th. Upper Devonian beds of southen area: adinole.
- 9 Thursday, April 16th. Carclaze, Luxulyan, etc.
- 10 Friday, April 17th. Roche and St. Stephen's
- 11 Saturday, April 18th.
Geologists' Association Circular No. 165. Session 1913–1914 p. 3–8
Easter excursions, North Cornwall, April 9th to 18th, 1914 - (transcribed from: GA Circular No. 165. Session 1913–1914 p. 3–8)
DIRECTORS: H. DEWEY, F.G.S., APRIL 9TH TO 15TH. T. C. F. HALL, F.G.S., APRIL 16TH TO 18TH.
EXCURSION SECRETARY: Miss G. M. BAUER, 16. Selborne Road, Handsworth Wood, Birmingham.
RAILWAY ARRANGEMENTS.—The party will leave London, Waterloo Station (L. & S. W. R.), on Thursday, April 9th, at 11.0 a.m. Luncheon Train. Due Camelford 5.28 p.m. Drive to Hotel, 9d. each. Special return tickets can be obtained from Miss Bauer, 26s. 4d. each. Special fare for the extension, Camelford to Bodmin and back, 3/2 each. For this excursion country members can obtain their vouchers from Miss Bauer.
HOTEL ARRANGEMENTS,—Camelford, April 9th to 15th. Headquarters ; Sunnyside Boarding House. Terms (including bed, breakfast, sandwiches for lunch, dinner, attendance and three drives) for the six days, 28/- per head. Shorter periods, 5/- per day. Members must be prepared to share rooms if necessary. Also The King's Arms Hotel ; terms for the six days, 2 2s. 0d. (including 3 drives) ; per day, 8/6.
BODMIN, April 15th to 18th. Headquarters: Royal Hotel, Bodmin, 9/- per day.
Accommodation at each centre being limited, members are advised to apply at once for rooms, stating that they belong to the G. A. party, and at the same time advise Miss Bauer that they have done so, giving particulars as to length of their stay and drives required and enclosing stamped addressed envelope for reply.
Early application is essential as it may be necessary to limit this excursion to members only. Miss Bauer can give particulars of apartments at both places to any who cannot get accommodation at the hotels.
A pamphlet descriptive of the geology of the districts is being prepared and will be on sale at the meeting on April 3rd, price to members 1/-, or by post from the Excursion Secretary 1/2.
The main object of the Excursion to North Cornwall is the study of the following: I. The Upper Devonian and the Carboniferous rocks and their relationship to one another ; 2. The structure of North Cornwall, the principal folds and the overthrust; 3. The pillow lava and associated rocks.
The structure of North Cornwall may be described, briefly, as an anticline on the north and a syncline, of St. Minver, on the south, with minor parallel fol 's between them, and others arranged tangentially to • their axes. These axes incline north. westwards ; at the nose of the anticline the tangential folds increase in amplitude and finally become overthrusts.
The Upper Devonian rocks occur as follows in descending order, the northern area being metamorphosed by a deep-seated igneous mass:
|! SOUTHERN AREA.||! NORTHERN AREA.|
|VI. Variegated slates (Famennian).||Tredorn phyllites.|
|V. Blue-black slates with goniatites (Frasnian).||Blue-black slates.|
|Trambley Cove Beds.|
|IV. Pillow lava.||Pillow lava.|
|III. Blue-black slates with goniatites (Frasnian).||Blue-black slates.|
|Barras Nose Beds.|
|II. Banded and striped grey slates.||Banded grey-green phyllites.|
|I. Grey-blue and grey slates with Spirifer verneuili.||Grey-blue and grey-green slates.|
|Delabole slate with Spirifer verneuili.|
The principal object of each day's excursion is printed in large type. Sections worth photographing are indicated thus (P), and localities where specimens should be collected are shown by letter (S)..
Good Friday, April 10th. Upper Devonian sequence and overthrusts
Breakfast 8 a.m. Start 9.15 a.m. Drive to Delabole Quarry. The Slate Company has kindly granted permission for the quarry and the works to be visited by the Association.
The slate is Upper Devonian and contains fossils, the commonest, Spirofer verneuili: being the "Delabole butterfly" (S). The quarry is 700 ft. deep and about half-mile long (P). The section shows bedding and cleavage dipping S.W. at 26° and 30° respectively. The slate is of two varieties, one, on account of its elasticity, durability and permanency of colour, is worked for roofing purposes ; the other variety being used for paving slabs and the like.
The plant used in dressing the raw material for the market will be examined.
Proceed to Trebarwith, noting sections of the Barras Nose Beds near the village, the pillow lava forming the crags on both sides of the deep valley near the sea, and the Trambley Cove and the Tredorn Beds at the Strand.
The sequence will also be studied at Port William and Trebarwith Strand, where the pillow structure of the lava is exposed (S). Several caves formed by the sea along faults occur at Dennis Point in the Tredorn Beds. After luncheot proceed along cliff path to Caroline Quarry, examining the normal sequence of bed: as far as West Quarry, where the Delabole slate first appears. Between West Quarry and Dria Quarry the Delabole slate was worked for many years in some huge excavations (P). Veins of albite and quartz occur in the slate. At Lanterdan Quarry the Woolgarden phyllites (S) first appear overlying the Delabole Slate, the whole mass having been overthrust upon the Trambley Cove Beds and the lava. The plane of overthrust, deeply scored with parallel strip, and hading gently N.W., will then be visited by descending a cliff path to Hole Beach (P and S). Return to Trebarwith for tea. Walking distance three miles. Dinner 7 p.m.
Saturday, April 11th. Upper Devonian sequence and overthrusts.
Breakfast 8 a.m. Start 9.15. Drive to Tintagcl. The village of Trevena, is built upon lava, and of this there are many sections. Follow path to the valley, where a stream has exposed the synclinal structure of the beds. Beside the path the Trambley Cove Beds dip north, and overlie lava; the beds then rise to the hotel, the dip being south. Below the Keep is a precipice which has resulted from erosion along a fault (P). The rocks are smashed into a structureless state and riddled with veins of quartz, and shear lenticles are well exposed near the archway of the Keep (P). The Barras Nose and Woolgarden Beds here overlie the Trambley Cove Beds and lava; which are seen at the base of the cliff, Descend to Tintagel Haven, whence a view of Tintagel Island and Barras Nose is obtained (13). In both of these headlands the overthrust masses are exposed, the beds being gently inclined but increasing in steepness towards the land, and finally rearing up on end at the point where they are thrust-over the rocks of the normal sequence in Trevena Valley. These vertical beds are seen below King Arthur's Hotel. King Arthur's Castle is built on Tintagel Island (P), and to reach it the steps will be ascended and the series of overthrust Upper Devonian Beds crossed.
The top of the island is all Tredorn Beds, but the underlying beds are exposed in the many crags, bluffs, and cliff faces.
There are several caves, including Merlin's Cave, in Tintagel Haven which have been caused by the sea acting along the thrust-planes. Barras Nose consists of two overthrust masses resting one upon another, but only the following beds are preserved. First the Barras Nose Beds overlain by lava, succeeded by the second overthrust mass of Woolgarden and Barras Nose Beds and lava. At the summit of the headland is a mass of rock consisting of quartz, calcite and magnetite which is highly magnetic. Members are requested not to destroy the section by collecting specimens at this locality.
Proceed along Smith's Cliff to Willapark, and thence to Bossinney Bay (P). Between the last two localities the whole Upper Devonian sequence is crossed, commencing with the Tredorn Beds and finishing with Woolgarden phyllites at Bossinney (S). Return to Tintagel for tea. Walking distance four miles. Dinner 7 p.m.
Sunday. No Official Programme.
A short walk will be taken in the morning to Tyland's Quarry to see the lime-silicate hornfels, with axinite on the joint-faces.
In the afternoon those wishing to do so will be able to visit Rough Tor (S and P) and the granite moors, returning by the Camel Valley, where elvan (S) is exposed, to Camelford for tea.
Monday, April 13th. Upper Devonian beds of southern area, pillow lava and associated rocks
Breakfast 8 a.m. Start at 9 a.m. sharp and drive to Church Hill Quarry, Port Isaac. A magnificent section of pillow lava, showing mass of thick-walled pillows, each consisting of concentric bands of solid and vesicular rock. Vesicles and hollow pillows are filled with calcite, chlorite, and quartz. Some contain black oxide of manganese ; chert also occurs (S).
Drive to Pentire Head to see the finest section of pillow lava in England (P). Members are requested not to destroy this section by attempting to collect specimens. Walk to Cliff Castle, examining on the way the grey-striped and black slates with Styliola and Tentaculites. A sill of albite-diabase has converted the slate into adinole and produced green garnets in a bed of limestone. The scenery is bold and grand (P and S).
Return to Pentire, and on to Polzeath and Trebetheric, crossing the northern limb of the St. Minver syncline. The variegated slates compose the cliffs around Polzeath Bay and contain Entomis serratostriata and Posidonomya venusta (S). At Trebetheric Point (P) the raised beach deposits will be examined. In descending order these are a boulder bed with erratic; slaty detritus or "head," cemented sands and beach resting on raised beach platform. The relation of this beach to that of South Wales, Southern Ireland, and to Palӕolithic man, will be discussed.
Proceed to Daymer Bay, where the Frasnian Beds, with many goniatites and other fossils, are faulted against the variegated slates with trilobites and brachiopods (S). The Doom Bar and a submarine forest will be inspected. Continue the walk to Rock, over a landscape buried under blown sand, which consists of the raised beach with old cliffs and headlands (P). St. Enodoc Church, partly buried in sand, will be visited. Rock Quarry is the type locality for Minverite (S). Quarrying has exposed a pitching anticline ; the beds are slate, limestone and adinole, in contact with a sill of Minverite, which weathers into spheroidal masses with exfoliating concentric skins.
Tea at Rock. Walking distance five miles. Cost of drive 4s. each. Dinner 7 p.m.
Tuesday, April 14th. Relations of Upper Devonian to Carboniferous Rocks: Pliocene features, and physiography
Breakfast 8 a.m. Start at 9 a.m. sharp. Drive to Rocky Valley. Visit St. Nectan's Kieve, a waterfall with a drop of about 50 ft. The fall is due to post-Pliocene uplift having produced hanging valleys along the cliffs. These valleys have since been cut back inland and the streams now form waterfalls. Examine pot-holes along gorge as far as the sea (P). Fine coast views (P). Walk along Trevalga Cliffs over lava, Trambley Cove and Tredorn Beds, noting influence of hardness of rocks on coast scenery. Visit Trewethet Quarry—a dyke of quartz and schorl (S). At Fire Beacon collect albite-felspar crystals, and fossils from the Tredorn Beds, which are here sprinkled over with rectangular white felspar crystals. Farther north, at Grower Gut, the junction of the Devonian and Carboniferous rocks will be studied (P). At Willapark (P) a fault throws down the Carboniferous rocks on the north (S); this fault face forms a magnificent scarp which runs inland to Forrabury Church as a bold craggy mass traversing the fields. A band of red volcanic rock is seen at Western Blackapit, but is decomposed and inaccessible. Boscastle Harbour (P) is nearly enclosed by a ring of precipices in which the great flat and zigzag folds of grit and huge veins of quartz are conspicuous (P).
Tea at Boscastle. Walking distance three miles. Dinner 7 p.m.
Wednesday, April 15th. Upper Devonian beds of southen area: adinole.
Breakfast 7.30 a.m. Drive at 8.20 a.m. with luggage to Camelford station, cost 9d. each. Train 8.57 a.m. to Padstow, arrive 9.41 a.m. Drive to Trevose Head.
Proceed to Dinas Head. Albite-diabase, adinole and limestone (S). The adinole is finely exposed and is spherulitic. The limestone contains masses of the coral Phillipastrea-hennahi. Walk along cliff to Merope Rocks (P), a reef of albite-diabase which has resisted erosion. At Cataclews (S) a fine-grained variety of Minverite has been quarried since the 14th century, and the stone is seen almost unweathered in many churches of the neighbourhood. At Harlyn Bay the Celtic Burial Place will be visited; here there are many stone cists which still contain skeletons of the late Stone Age, and there is also a museum of antiquities. Trevone Bay (S) consists of grey slates with many goniatites, Buchiola retrostriata, Bactrites, etc. (Frasnian Beds). Continue walk to Round Hole (Minverite), a cave with a fallen roof, to Porthmissen, where the famous Marble Cliffs occur (P), which consist of alternate beds of slate and limestone with a gentle dip. These beds form the southern limb of the St. Minver syncline—the northern limb occurring between Pentire and Trebetheric.
Drive to Padstow for tea. Walking distance four miles. Cost of drive 2s. each.
Leave Padstow Station 5.50 p.m., arrive Bodmin 6.24 p.m.
Dinner, Royal Hotel, 7.30 p.m.
Thursday, April 16th. Carclaze, Luxulyan, etc.
Breakfast 8 a.m. At 9.15 a.m. drive to the Lantern Clay Works and examine a typical clay-pit, together with the various processes used in the recovery of the china-clay from the decomposed granite ; these may be specially well seen at these works owing to their compact and systematic arrangement. Abundant tourmaline is present in the clay of this locality, and a striking feature is the large wall-like mass of quartz-tourmaline-rock or " stent " left standing in the pit. Then proceed to the Bunny Clay Pit, where veins of schorl-rock and greisen may be seen. Search for specimens of gilbertite and large well-shaped "pseudornorphs" of kaolin and mica after orthoclase. Near by is Caudledown Pit, an immense excavation, worked by three companies, half-a-mile in length and over 300 ft. deep. From here drive to Carclaze Downs and visit the large pit worked by Messrs. John Lovering & Co. In the older portion of this pit veins of schorl-rock are remarkably abundant, many of which are stanniferous. On the east side of that part of the pit now being worked can be seen a basin of solid granite resting upon the kaolinised rock, and extending downwards for about 20 ft. from the surface.
From Carclaze drive to Luxulyan and visit the large granite quarries of Gready, Cblcerrow, and Golden Point. The rock of these quarries is a typical Cornish granite, with two micas, and contains andalusite, cordierite, and pseudomorphs of pinite. Inclusions of killas (xenoliths) are well displayed at Golden Point. Veins of pegmatite occur, which should be carefully searched for cavities containing well-formed crystals of orthoclase, albite, quartz, gilbertite, apatite, tourmaline, fluorspar, and muscovite.
Tea at Luxulyan. Total driving distance about twenty miles. Cost of drive 3s. each. Dinner 7.30 p.m.
Friday, April 17th. Roche and St. Stephen's
Breakfast 8 a.m. At 9.15 drive to St. Dennis and examine the mica vein of Trelavour Downs ; this contains coarsely crystallised lithium-bearing biotite. Thence continue the drive to St. Stephen's, and visit the china-stone quarries of Tregargus, where good specimens of the various types of rock, some showing abundant visible fluorspar, may be obtained. The various processes used in the treatment of the stone for the market can also be examined. From St. Stephen's .return to Roche, visiting on the way, if time permits, Carpalla Clay Pit and St. Mewan Beacon. At the former is a fine section showing the occurrence of kaolinised granite beneath an overburden of killas, while at St. Mewan Beacon are to be obtained excellent examples of schorl-rock of various kinds. At Roche is to be seen the well-known mass of schorl-rock known as Roche Rock, which forms such a marked feature of the district. This rock forms an apophysis from the main granite mass to the east, Fine specimens, showing variable amounts of quartz and tourmaline, may be collected. At Tresayes Downs, close by, is an old quarry in a very coarse pegmatite, formerly worked for use in the manufacture of glass. The quarry is now, unfortunately, full of water, but specimens showing large felspars, quartz, tourmaline, fluorspar, etc., may be obtained from the spoil heaps.
Tea at Roche. Total driving distance about twenty miles. Cost of drive 3s. each. Dinner 7.30 p.m.
Saturday, April 18th.
In the morning, by the courtesy of Sir William Serjeant, C.B., members of the Association may inspect the fine collection of Cornish and other minerals at St. Benets Abbey. The specimens of cassiterite, in its various forms, are especially interesting. Examples of luxulyanite and other Cornish rocks may be seen also.
Return trains, Bodmin 12.37 a.m., arrive Waterloo 8.7 p.m.; . also Bodmin 2.19 p.m., arrive Waterloo 10.34 p.m.
1909. Geological Map, Bodmin area, 1-inch scale, colour-printed (H. M. Geological Survey), Sheet 347. Price 1s. 6d.
1909. "The Geology of the Country around Bodmin and St. Austell," by W. A. E. USSHER, G. BARROW, and D. A. MACALISTER, with Petrological Notes by J. S. FLETT (Mem. Geological Survey). Price 4s.
1910. Geological Map, Camelford area, 1-inch scale, colour-printed (H.M. Geological Survey). Sheets 335 and 336. Price 1s. 6d. each.
1910. "The Geology of the Country around Padstow and Camelford," by C. REID, G. BARROW, and H. DEWEY, with contributions by J. S. FLETT and D. A. MACALISTER (Mem. Geological Survey). Price 25. 3d.