SLATE QUARRIES are noticed in a separate article.
The atone most extensively diffused over Euglaud and Ireland is that which is denominated limestone, and which, from the facility it affords working it, is most generally called freestone. It is quarried to some extent in Gloucestershire, Shropshire, Derbyshire, and Oxford shire, and a gray species is obtained in Yorkshire and Northampton shire ; but the principal quarries 01 this material are in Dorsetshire and in the country about Bath. Those in Dorsetshire are situated about Kingston in the Isle of Portland, and at Swanwich, or in the Isle of Purbeck. The most extensive quarries about are at Combo Down, where the ground has been undermined for several *miles. More than 30,000 tons of Portland stone are said to be ex ported annually to London, where it has been very generally employed from the time that Inigo Jones used it in the construction of the Banqueting-house at Whitehall. It was also extensively used by Sir Christopher Wren in the building of St. Paul's cathedral, the 3lonu rnent, and most of the public edifices in the city after the great fire which occurred in 1666. It is, however, not so much used at present as formerly. The stone obtained from Purbeck is of various kinds; some of it, which is capable of taking a good polish, has been used for the pillars of Salisbury and Canterbury cathedrals. It is of a darker colour than Portland stone, and in general it is not so good; the blocks raised from the quarries are also smaller. The material is frequently used as a flag-stone for the steps of buildings and for paving the streets. The hills containing the stone lie in a direction nearly east and west ; the beds have a considerable dip or inclination to the horizon, and being covered by a largo mass of earth, the men work in quarries under ground. The stone of Portland and Purbeck constitutes the upper oolite formation of the geologists; and in the former district the quarries are cut through several different beds. The first, or that Immediately below the vegetable earth, consists of a cream-coloured limestone, three or four feet deep ; end next to it is the cap-stone, which is of the same colour, very hard, and about ten feet thick.
Below these is a species of rock composed of fragments of oystenshells cemented together; and still lower Is a bed, five feet thick, of good white stone. This is followed by a quantity of flint about six feet deep, a second bed of good stone fire feet deep, and a thin layer of stones of small value. The best building-atone lies still deeper, and the beds of it vary in thickness from seven to fourteen feet. Under neath all these are masses of flints, extending to the depth of fifty or sixty feet.
The quarries near Bath furnish the stone which bears the name of that town, and which occurs generally in three beds, of variable thick nesses and different qualities. That in the middle is far superior to those which are above and below it.. The depth of the middle bed is in some places as much as 30 feet ; the stone when first taken from the i quarry is soft, but it becomes hard after having been for a time exposed to the air. The depth of the upper bed varies from 20 to above 50 feet, and the material is either mildly or argillaceous; that of the former kind appears to have been employed by the Romans for the edifices they constructed in this part of the country, and is very durable.
The marble and limestone quarries which were opened near Plymouth in 1812 furnished the material used in the formation of the breakwater at that place • the Skill() was raised from thence in blocks weighing from one to five tons. The material selected for the con itruction of the Houses of Parliarneut is a magnesia(' limestone, which 'bounds in all the tract of country from Durham to Northampton ; and that which is actually employed is obtained from several differ ent quarries, principally those near Norfall and Anstou in Yorkshire, and near Bolsover in Derbyshire. The unfortunate result of this selection will be found noticed under STONE Foil BUILDINO.