ROOFING SLATE. 79 
oils, are made of a particular kind of slate, that, on 
splitting, falls into long splintery fragments. It is 
necessary that the pencils should be considerably softer 
than the slate to be written upon, so that they may 
leave a whitish streak on its surface, without scratching 
it. Such is the shivery nature of the slate of which 
they are made, that, if it be exposed for some time to 
the action of the sun or frost, it is rendered useless. 
Hence, workmen are careful to cover it up and sprinkle 
it with water, as soon as it is taken from the quarry, 
and to preserve it in damp cellars. The pieces are 
afterwards split by a particular instrument, and then 
wrought into the requisite shape. 
In some of the quarries in Derbyshire and Wales the 
slate is so thick as to admit of being split into large and 
tabular pieces. These are used for gravestones, and for 
slabs for dairies and cellars. Paving stones and mile- 
stones are also formed of them ; and vessels for the salt- 
ing of meat, and setting of milk in dairies. For the lat- 
ter use slate is peculiarly well adapted, on account of 
its resistance of greasy or oily substances. But this 
property renders it unfit for any purpose for which it is 
requisite to be painted ; as, the oil not entering the 
stone, the paint soon peals off, and leaves the stone as 
black as it was at first. Cut into narrow, strips, slate has 
also been applied, in the neighbourhood of Bangor, 
North Wales, for the formation of fences. 
When sufficiently solid for the purpose, slate is cut 
into inkstands, and turned into vases, and fancy articles 
of various kinds. And a singular circumstance has been 
remarked, that, if a window or door be suddenly opened, 
in an apartment where the workmen are turning these, 
they will sometimes fly in pieces ; though, after the 
work is finished, they may be exposed to the usual 
changes of temperature without injury. 
Pounded slate is advantageously used for cleaning 
iron and other works in metal. When well ground, and 
mixed with a certain proportion of loam, slate is made 
into moulds for the casting of metals in ; and, when 
