Odd rocks of the Scilly Isles

BGS Image ID: P241716

The 'Loaded Camel' St. Mary's.

BGS Image ID: P241720

The 'Nag's Head' St. Agnes.

BGS Image ID: P241717

The 'Punch bowl' St Agnes.

A series of photographs taken by R.H. Preston illustrating weathering of granite. The photographs were donated to the British Association for the Advancement of Science Collection. Photographs are dated 1895.

See also 'The Drum Rock'
Posted by Bob McIntosh

English churches - building stones

BGS Image ID: P209976

Drewsteignton village square, Devon. Looking east. Drewsteignton village is sited high on the northern edge of Dartmoor. Holy Trinity Church and Church House with its large chimney stack are both built of Dartmoor granite blocks. Drewsteignton village is typical of many on the the northern fringe of Dartmoor. The church tower is built of Dartmoor granite (imported to the district). The house to the right of the lych gate is built largely of rough hewn granite blocks. The wall to the left of the lych gate is built of blocks of impure limestone and hornfelsed mudstone from the local quarries (now disused). The granites of Devon and Cornwall and their associated intrusive and metamorphic rocks have commonly been worked in the past for building stone, both for local housing and for major building projects elswhere in the United Kingdom such as the many 19th century dock construction schemes in London.

BGS Image ID: P210728

Snettisham Church, Norfolk. Looking east. This large, late medieval church at Snettisham is typical of many in this area where a mixture of local building stones are used for the main walling material, chalk, flints and ferruginous carstone, with better quality oolitic freestones of the Lincolnshire Limestone Formation imported for more ornate mouldings and carved stonework. Built in the 14th century decorated style, Snettisham Church has its nave and tower constructed of partially dressed blocks of chalk and flint. The spire, pinnacles, copings, buttresses and window tracery are made of oolitic limestone, one of the Middle Jurassic freestones. The wall in the foreground is made of dressed Carstone blocks which have suffered some frost damage. While this area of Norfolk produced a wide variety of local building materials, including sandstones, limestones and flints, none were good enough to qualify as freestones. Consequently from medieval times onwards the oolitic limestones of Lincolnshire were commonly imported for the stonework in all the more prestigious buildings.

BGS Image ID: P210855

St Mary's Church, Purton, Wiltshire. Looking north-west. This Norman / Medieval church with its spire and crossing tower is constructed of Jurassic Coral Rag limestones. The term Rag refers to the coarse grained shelly (or ragged nature) of the limestone when fractured. The ragstone beds are generally very hard and durable stones but are consequently, therefore, very difficult to work, commonly they are used as undressed rubblestone blocks. This church at Purton is largely built of local 'Coral Rag' Limestone from the local Osmington Oolite Formation.The roof of the church is covered with stone slates which in this area are likely to be from the Forest Marble Formation, although some use of local Purbeck limestones is also known. The hard, pale grey, coarsely oolitic and shelly limestones of the Corallian Group were widely used in buildings along their outcrops in Dorset, Wiltshire and Oxfordshire.

Posted by Bob McIntosh

Granite from Ailsa Craig, Scotland

BGS Image ID: P521397

Rock specimen of riebeckite granite. Ailsa Craig, Firth of Clyde, Ayrshire, Scotland. British Geological Survey Petrology Collection sample number EMC3360.

The sample is a pale-coloured coarse-grained igneous rock with a distinctive granitic texture. It is technically a microgranite dominated by pale alkali feldspar crystals embedded in dark riebeckite amphibole and grey quartz.  The distinctive granite of Ailsa Craig forms part of the vast Tertiary Igneous Province of northern Britain. These formed around 60 million years ago. Much of the distinctive scenery of areas such as Arran, Mull, Ardnamurchan, Rum and Skye, and the Antrim Mountains in Northern Ireland, were formed as a result of this huge outpouring of magma. Because these rocks are well exposed and preserved they have been studied in great detail by generations of geologists, and provide an opportunity to study the deeper levels or 'roots' of volcanoes, from which we can learn much about currently active volcanoes today. The riebeckite granite of Ailsa Craig forms a Tertiary granite boss rising out of the Clyde estuary. It is one of a series of Tertiary granites. This blue-grey microgranite is very distinctive and has been extensively used as a marker for tracing the flow directions of Quaternary ice-sheets.

BGS Image ID: P750285

Another specimen of granite from the Ailsa Craig Quarry. British Geological Survey Petrology Collection sample number Econ. 1166.

BGS IMage ID: P001614

View of the old Ailsa Craig curling stone quarry situated on the north coast, Strathclyde Region, showing drilled-out stones 28 cm. in diameter in microgranite. 

The stone has a tough fine-grained lithology and can take a very high polish. It was worked in two colours, the 'red' and 'blue' varieties, the former was rarer and was much preferred. The curling stones were the economically most significant and world-renowned resource of the island. 50 pairs were exported annually in the 1870's rising to 1000 pairs in the 1890's. The quarry restarted 1961 but becoming uneconomic closed again in 1973.

BGS Image ID: P000704

BGS Old photograph number: D02015

Oblique aerial view of the island of Ailsa Craig. Looking south towards the north end of the island. The island is a very prominent landmark in the Firth of Clyde formed of a microgranite boss. Ailsa Craig is formed of an arfvedsonite-aegirine-microgranite intruded by vertical dyke swarms of olivine to alkaline olivine-dolerite with basalt margins. Isotopic dating using the Rb/Sr isochron method dates the microgranite at 61.5 Ma. This makes it Tertiary in age. The remains of the castle can be seen on the skyline on the left. It was built on the orders of the Earl of Cassillis by Thomas Hamilton whose coat of arms may be seen on the walls.

The resistance of the microgranite to erosion compared to the response to the soft Permo-Trias sandstones into which it was intruded was of crucial importance during the phase of glacial erosion. The principal direction of the ice during the last glaciation was south. This is indicated by the slight broadening of the island from north to south, albeit that this outline has been considerably modified by later marine action. The precipitous cliffs are primarily the results of marine erosion but the initiation of a strongly positive topographic feature associated with the microgranite intrusion probably occurred during glaciation.

Posted by Bob McIntosh

Kemnay Quarries, a working granite quarry, 1939.

BGS Image ID: P000136

Kemnay Quarries. Aberdeenshire. General view of the mason's yard. Stockpiled finished stone in a variety of sizes all neatly labelled can be seen in front of the masons' sheds. A steam train is seen mounted on a light railway. In the distance is part of No. 2 Quarry with several blondins stretched across the quarry. The roofs of the sheds could open to allow the travelling steam crane to deposit stone inside for the masons to work on.

BGS Image ID: P000132

Broken granite blocks after blast. Three quarrymen working at splitting a large block, one is wielding a pneumatic drill while the other two are using large crowbars.

Date of photographs: 1939.

An earlier post on Kemnay can be viewed here

Posted by: Bob McIntosh

St. Austell Granite from Gready Quarry. 1914.

Crystals of orthoclase with inclusions of biotite

 Crystals of orthoclase with inclusions of biotite

Twinned crystal of orthoclase

 Quartz-tourmaline rock or 'stent'

Photographs are from the Geologists' Association 'Carreck Archive' held at the British Geological Survey.

Posted by Bob McIntosh

Splitting a granite block using the plug and feather technique, Rubislaw Quarry, Aberdeen

BGS image ID: P538600

Splitting a granite block using the plug and feather technique. Tapping home the peg. Rubislaw Quarry, Rubislaw Granite Co. Ltd., Queens Road, Aberdeen. Date: c. 1961.

From the Hugh O'Neill Collection.

Bob McIntosh

Granite dressing sheds at De Lank quarries, St. Breward, Cornwall

BGS image ID: P000510

Granite dressing sheds at De Lank quarries, St. Breward, Cornwall. Looking west-north-west.
The De Lank quarries work the coarse-grained, grey granites of Bodmin Moor. The extensive range of granite products on display in the De Lank dressing sheds is a tribute to the skills of the masons who originally worked this hard intractable stone with only limited hand tools. Since the 15th century granite has been used in buildings as hewn blocks and cut into ashlar. Also, up to about 1800, granite was taken from the vast amounts of surface debris. More recently there was demand for building blocks of ground 'reconstituted' granite where planning regulations demanded the use of stone. The De Lank Quarries near Bodmin produced a light grey granite. Large blocks were obtained from the quarries because of the regular jointing. The Eddystone, Beachy Head and Small Rock lighthouses are among many buildings constructed from De Lank granite.

Old BGS photograph number A00517

Date of image: 1907

Bob McIntosh

The 'Drum Rock', St. Mary's, Scilly Isles. Weathering of granite.

BGS image ID: P241718

The Drum Rock', St. Mary's. Scilly Isles. Weathering of granite.

Dated 1895. Entry in BAAS Report for 1903. Photographer: R.H.Preston, Alverne House, Penzance. Original format: Full plate. From the British Association for the Advancement of Science (BAAS) photographic print collection.

In 1888, a photographer, O.W. Jeffs proposed to the BAAS that they should address the need for systematic photographic coverage of the geology of the United Kingdom. His proposal was accepted and the BAAS set up a committee under the chairmanship of James Geikie, for the ‘collection, preservation and systematic registration of photographs of geological interest in the United Kingdom’. The collection soon expanded and was housed in London, first in the Geological Survey and Museum Library at Jermyn Street and later at the new premises in Exhibition Road, where it complemented the Survey's own collection of photographs. The BAAS committee arranged the sale of prints and lantern slides, and every year lists of photographs were published in the BAAS Transactions.

The collection at BGS consists of over 7,000 photographs from an original total of over 9,000. Most photographs covering Ireland are held at the Ulster Museum and a few albums, Dorset, Hampshire, and Lancashire, remain unaccounted for - does anyone know where they are?

Bob McIntosh