- Foremost among the useful products of the Carboniferous rocks is the coal (q.v.) itself; but associated with the coal seams in Great Britain, North America and elsewhere, are very important beds of ironstone, fire-clay, terra-cotta clay, and occasionally oil shale and alum shale.
The imports of ore in that year amounted to 1,862,444 tons of the value of £1,420,379 The oil shale industry is wholly modern and has attained to considerable magnitude since it was established (in 1851 and following years).
Also, in areas where the lightweight properties of the fill do not offer advantages, the PFA was replaced by spent oil shale.
To date no company has been able to get oil out of oil shale at a profit.
The oil shale bings of West Lothian have also accrued considerable heritage value.
Its primary ingredient is ichthammol, which is derived from the distillation of oil shale.
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