Sir Joseph Banks, to whose indefatigable ardour for the advancement of natural history, the philosophical world is so much indebted, made a voyage to Iceland in the year 1772, to enquire into the productions of that remote part of the world, and particularly into those of its famous volcano. When he returned, he brought from thence, among many other natural productions, some petrified vegetables, and incrustations, formed by the waters of the boiling springs; and he was so good as to present a part of them to his friends here, who were surprised to find them composed of siliceous earth. As this was the first example observed, of water containing this earth in such quantity as to form siliceous petrifactions, it raised a strong desire to have an opportunity of examining the water, and of learning by what means this siliceous matter was dissolved in it; and this opportunity was at last given us by John Thomas Stanley, Esq; who, excited by motives similar to those of Sir Joseph Banks, equipped likewise a vessel, and made a voyage to Iceland, during the summer 1789.