Geology of the country around Harlech : memoir for 1:50000 geological sheet 135, with part of sheet 149 (England and Wales)

SUMMARY The Mawddach Group is a new name for the rocks of late St. David’s to Tremadoc age in the Harlech Dome, previously called Menevian Beds, Lingula Flags and Tremadoc Slates. It follows conformably the Harlech Grits Group and is unconformably overlain on the eastern side of the dome by the late Tremadoc Rhobell Volcanic Group and elsewhere by sedimentary and volcanic rocks of Arenig age. The Mawddach Group comprises four formations, from bottom upwards called the Clogau, Maentwrog, Ffestiniog Flags and Cwmhesgen (new name). They are formally defined here for the first time and the stratigraphical nomenclature used in this area is revised. The group consists of about two kilometres of predominantly grey argillaceous rocks interbedded at intervals with quartzose sandstone and siltstone. Sedimentary structures show that the group represents a complete cycle of basin formation and infilling. The topmost formation, which consists of the Dolgellau and Dol-cyn-afon (new name) members contains new evidence of volcanism in the late Cambrian. The biostratigraphy of the group is considered in detail. Many of the zones of the Scandinavian succession are recognisable in the present area, but the brachymetopa Zone appears to be absent and some other zones remain unproved; the Acerocare Zone, however, is here demonstrated for the first time in Great Britain.

10.1144/pygs.43.3.295

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Geology of the Bristol district. Memoir for 1:63 360 geological special sheet (England and Wales)

G. A. Kellaway Francis Bryan Awburn Welch

New england

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Geology of the country around Warwick : memoir for 1:50000 geological sheet 184 (England and Wales)

Robin Anthony Old M.G. Sumbler Kirk Ambrose

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Geology of the country around Grimsby and Patrington. Memoir for 1:50 000 geological sheets 90 and 91 and 81 and 82 (England and Wales)

N. G. Berridge James William Pattison

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Geology of the country around Southampton : memoir for 1:50000 geological sheet 315 (England & Wales)

HMSO eBooks (1987)

R.A. Edwards E.C. Freshney

New england

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Geology of the country around Settle : memoir for 1:50000 geological sheet 60 (England and Wales)

HMSO eBooks (1988)

Russell S. Arthurton Emily Johnson D. J. C. Mundy

New england

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Geology of the country around Lewes : memoir for 1:50000 geological sheet 319 (England & Wales)

HMSO eBooks (1987)

R. D. Lake

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The Harlech Dome, north of the Barmouth Estuary

Quarterly Journal of the Geological Society (1946)

Charles Alfred Matley Theodore Stacey Wilson

Summary The area described, 150 square miles in extent, lies between the Barmouth estuary and the Vale of Ffestiniog and contains some 10,000 feet of Cambrian rocks which range from ?Lower Cambrian to Ffestiniog Flags and include thick formations of grit. The igneous rocks are all intrusive, are of Lower Palaeozoic age (though of more than one date), and are nearly always found in an altered condition; they are " greenstones " of either dioritic or basic composition. Quartz veins and metalliferous lodes are common. The sediments, the materials of which are chiefly derived from an easterly extension of the Mona Complex of Anglesey and south-western Caernarvonshire, have undergone low-grade metamorphism; some beds (especially the Manganese Ore Bed) are rich in authigenic spessartite. The general structure is a broken anticlinorium which has been compressed from west to east. The cleavage is predominantly northerly. Faults are numerous, the latest being an important north-and-south series with displacements up to about 4000 feet.

Dome (geology)

10.1144/gsl.jgs.1946.102.01-04.03

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Citations (54)