Note 39 — Chapter XXIX · THE CARBONIFEROUS VOLCANOES OF ENGLAND

A difference is made by the mining community between "toadstone" and what is called "blackstone." The former name appears to be restricted to the amygdaloidal green and generally more or less decayed lavas; the latter, so far as I can learn, is applied to the dark, more solid and crystalline rocks. If this distinction be well founded the one name may perhaps serve to mark the open cellular lavas, the other the more compact, dark, and heavy intrusive sheets.