Eruptive rocks of Brent Tor by Frank Rutley, 1878.

Plate VIII. 
Basalt with glassy magma mainly devitrified. Brent Tor, North-west side of the foot of the Tor, Magnification x55.

The 'Eruptive rocks of Brent Tor and its neigbourhood' was the first special petrographical work issued by the Geological Survey. It is dated 1878.  It denotes a time when microscopic examination of rocks collected during the mapping of new districts became routine. Colour chromolithographs.

Frank Rutley was also the author of Elements of Mineralogy first published in 1874 and still available in print today in its 27th edition!

Plate IX.
1. Decomposed Greenstone, Greston Bridge.
2. Slate beneath lower Greenstone, Greston Bridge.
3. Elvan, S. end of Shilla Mill Quarry (Polarized).
4.Mag'n. Mica and cavities in Quartz of Granite, Brazen Tor.
5. Fluid cavities containing cubes of NaCl, Brazen Tor.
6. Amygdaloidal Schalstein, Churlhanger, near Lamerton.

Plate X
No. 1 Hornblende, Pyrites and Quartz in Amphibolite, Brazen Tor, Devon
No 2 Schorl in the Granulitic margin of the Granite in contact with No. 1
No 3. Pyroxene (probably Diallage) in Gabbro? Cottage Inn, Main Road to Marytavy.
No. 4 Titaniferous Iron, partly altered (Gabbro) Cock's Tor, near Tavistock.
Bo. 1 x55. Nos. 2,3 and 4 x25. ordinary transmitted light. On the surface of No. 4 a little light was also reflected simultaneously.

Brent Tor. (South side near the base) x25
Brent Tor. (North side) x25

A selection of plates from the memoir:

Brent Tor from Hart's Hall, near Morwellham

 Great Staple Tor on the western Margin of Dartmoor (mural jointing in granite).

The Master Rock, Horndon. (woodcut)

Posted by Bob McIntosh

China-clay works, Devon and Cornwall

BGS Image ID: P200171

Lantern China-clay Works, near Rescorla, St. Austell. Looking SW. View of lower part of clay-pit. This photograph, taken down in the pit, shows the stream of water, by which the clay is washed out of the decomposed granite travelling down the stope and from thence through the sand-pits to the 'bottom hole launder', whence it is pumped to the surface. The sand-pits are only partly visible in the photograph, but the annexed diagram shows the direction of flow of the water.

BGS Image ID: P200203

Hendra Downs China-clay Works, St. Dennis. Looking N. Team and waggon with load of clay.

BGS Image ID: P2009710

Old photograph number: A09799   1962

China clay workings, Great Pit, Lee Moor, south Dartmoor. General view of china clay-pit showing systems for disposal of waste sand; (1) right, old inclined railway to large 'burrow', and (2) left, new covered conveyor belt to small burrow (sited on ground having low clay yield). China clay is formed by the kaolinization of granite, a process of late hydrothermal alteration where acid solutions moved along the joints in the granite and caused the plagioclase feldspars to be converted to kaolinite. The name kaolin comes from the mountain Kauling in China where the material was discovered. Large scale exploitation began in the 18th century. Recently the industry has become intensively mechanized.

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