Geological Position

This stone is obtained from that division of the Oolitic formation which is known as the Great or Bath Oolitic group. Geologically speaking it lies below the Portland stone, being separated from it by the Kimmeridge clay, coral rag, and Oxford clay.

The building stone lies between beds of Tagstone: dark veins run at right angles to the beds.

Most of it is of a fine even grain, composed chiefly of carbonate of lime - sometimes interspersed with shelly fragments.

Some of the varieties of this stone contain sand-cracks, vents, clay-balls, etc.; these should of course be avoided.

Colour

The colour varies from white to light cream colour and yellow.

Quarrying

The quarries are worked by tunnelling, and the stone is produced in blocks up to 5 or 6 feet deep, and weighing as much as 10 or 12 tons.

It is important that Bath stone should be quarried in summer when it is freed from the ground moisture or quarry sap. If quarried in winter it is very likely to fall to pieces with the first frost.

Seasoning And Weathering

The stone is very soft when first quarried, but hardens upon exposure to the air (see p. 49). It is important that it should be placed on, or parallel to its natural bed (see p. 9).

The stone varies greatly in quality: some varieties weather badly, while others are fit for external work in ordinary atmospheres.

Size And Uses

As it is obtainable in large blocks, and is easily worked, it is particularly valuable for mouldings and carved work.