Header laying. - Thin dark stone used for headers.
10 inches thick; greenish colour; free working; not very sound. Fossils generally found on top bed. Below this is a layer of workable hassock.
Broken up into headers for pitching.
Pelsea yields large hard blocks 12 inches thick; difficult to quarry.
Next come two inferior and flinty beds interspersed with hassock.
Great Rag is a layer sometimes 3 feet deep, but split into two thicknesses full of cross fissures; no large stones from it. Broken up for header?, or makes the best description of lime. A very superior layer of hassock (often containing fossils) is found below this bed.
A flinty bed; produces some large blocks. Then a flinty bed. between two layers of hassock.
Whiteland Bridge produces blocks 12 feet long, any width, and 14 inches thick; stone very free working; bluish colour.
Like the last bed, but of small scantling. Used for paving kerbs. After the last bed comes some inferior hassock.
Horse Bridge yields blocks of good stone, 15 feet long and 16 inches thick.
Headstone laying yields blocks about 7 inches thick, used for headstones. Then a deep bed of soft hassock.
White Rag, which is of no use for building, as it tumbles to pieces upon exposure to the air.
The Ragstone is used chiefly for rubble work, being very difficult to dress. It does not gain in beauty by being tooled, because even the best kinds are full of small hassocky spots, which show themselves upon a smooth face, turn rusty upon exposure to the weather, and facilitate the decay of the stone.
If used as ashlar, great care must be taken to place it on its natural bed, otherwise it will decay.
The ragstone is not suitable for internal work, for, as it is non-absorbent, the moisture of the air condenses upon its surface, causing what is known as sweating.
All ragstone used for external work should have the hassock carefully knocked off.
It is important also to see that the small "pockets" containing iron, which often occur in the stone, are not exposed upon the face, otherwise the iron will oxidise upon exposure to the atmosphere, and cause ugly rust stains.
There are several quarries, among which may be mentioned the Iguanodon, Chillington, Allington, all near Maidstone. Also quarries at Aylesford and at Boughton.
The following are analyses of the Kentish Rag and Hassock respectively :-
Carbonate of lime with a little magnesia..
Oxide of iron........
Carbonate of lime ...
Oxide of iron..
Yellow Mansfield, is obtained from quarries at Mansfield Woodhouse, two miles from Mansfield. It is crystalline, and has a warm yellow colour.
This stone almost exactly resembles the Bolsover Moor stone, which was selected by the Royal Commissioners for the Houses of Parliament.
The only difference is "that its colour is rather deeper, partly owing to its having a greater number of minute black specks, which is a peculiarity more or less to be found in all varieties of the magnesian limestone rocks."
The chemical composition of Mansfield stone, and the characteristics which it shares with other magnesian limestones, are given at pages 58, 59.
It is useful for ashlar, mouldings, columns, etc., and is eminently adapted for highly carved work.
Where used. - Amicable Life Assurance Office, Fleet Street Martyrs' Memorial, Oxford.
Caen and Aubigny Stones are Oolitic limestones, which may be mentioned here, as they are a good deal used in this country, though they are found in Normandy.
Caen Stone is of a pale cream-yellow colour. It is very soft when first quarried, but hardens upon exposure; is easily worked and carved, but weathers very badly; weighs 120 lbs. per foot cube. Used in Henry VII. Chapel, Westminster Abbey; the Tower, Buckingham Palace, and many other buildings.
Aubigny Stone is similar to Caen, but more crystalline, harder, and heavier. It also weathers badly. Used at St. Mary's, Stoke Newington, and other buildings.
Several other limestones of considerable importance will be found in the following Tables:-