Sir Richard Francis Burton,
Ultima Thule; or, A Summer in Iceland…
“ The Solfataras.—Sulphur is formed by certain gases generated underground by volcanic action, and in solfataras these gases find their way to the surface of the earth through sand, ashes, or other volcanic substances, and in their passage sublime and deposit a certain portion of their sulphur, a certain amount escaping into the air.This formation of sulphur is continuous and increasing, and in proportion to the strength of the volcanic influences so is the rapidity with which the sulphur is formed and the amount taken from the solfatara replaced. For this reason they are called “living.” ”
