Besides the small thin slates used for roofing, large and thick slabs, and even blocks of slate, are quarried out and used for many purposes connected with building and engineering works.

Slate in these forms is particularly useful on account of its strength. " The strength of slate 1 inch thick is considered equal to that of Portland stone 5 inches thick,"' and " its resistance to shearing is said to be greater than that of any other stone." 2

Slate slabs are easily obtained of any length under 6 or even 8 feet, and containing from 10 to 30 superficial feet.

Their thickness ranges from 1 inch to 3 inches.

Larger slabs may be obtained by paying extra. The Exhibition of 1862 contained one sent by the Llangollen Slate Company which measured 20 x 10 feet, and weighed 4 1/2 tons; also several from the Ffestiniog quarries of the Welsh Slate Company averaging 14 feet by 7 or 8 feet.3

They may be procured either self-faced - that is, as they are split from the blocks - rough sawn, quarry planed, or polished.

The edges are sawn square, planed, filed, or rounded.

Such slabs may be fitted with great accuracy, and are used for cisterns, urinals, troughs, mantelpieces, baths, window and door-sills, skirtings, flooring, wine-bins, steps, landings, etc.

Slate Blocks, containing as much as 2 or 3 cubic feet, can easily be obtained.

In Wales and other slate districts they are sometimes used for the walls of buildings, and slate in scantlings is substituted for much of the wood work, e.g., in door and window frames.

Slate is also sent out from the quarries in the form of steps, sills, etc.

The same material is used for making ridge rolls of different patterns for roofs, dowels for heavy masonry, etc. etc.

Enamelled Slate is prepared by painting slate slabs, baking them, colouring to pattern, covering them with a coating of enamel, rebaked and rubbed down several times alternately, and then polished.

It is often made to represent different varieties of marble, and is much in request for chimney-pieces and other purposes for which marble is used, also for sanitary purposes.

Varieties In Use

There are many slate quarries throughout Great Britain and Ireland, on the Continent, also in Canada and the United States.

Some American slates have been imported during late years, but the great bulk of the slates used for building are from home quarries.