draw slate

draw slate

[′drȯ ‚slāt]
(mining engineering)
A soft rock, 2 inches to 2 feet (5 centimeters to 0.6 meter) thick, that lies above a coal seam and falls with the coal as it is excavated, or soon after.
References in periodicals archive ?
The creative students from Coleg Menai, near Bangor, have been commissioned by the BBC to draw slate signs for Britain's Strongest Man, to be filmed at Criccieth Castle tomorrow.