human
Recent operations have from time to time disclosed old workings which have obviously been made at a very early period, by the primitive method of lighting great fires upon the veins containing ore and, when sufficiently heated, pouring cold water upon the rock, and so, by the sudden abstraction of caloric, rending, cracking and making a circumscribed portion workable by the rude implements then in use, specimens of which are still found occasionally in the very ancient parts of the mines, especially small quadrangular wedges perforated for the reception of a handle.