Small pack of timber consisting of a number of timbers laid side by side to form a solid mass 2 to 2-1/2 ft square by 4 to 6 in thick (approx. 0.7 m square by 10 to 15 cm thick). Holes are drilled edgeways through the mat, and wires are threaded through to hold it together. Mats are transported underground and built up to form very effective supports.