Being a keen observer of natural objects and phenomena, he had noticed that on a certain part of his Guisborough estate the soil never froze, that it was speckled with divers colours, chiefly yellow and blue, which sparkled in the sunshine, and that the trees and shrubs which grew thereon spread their roots laterally, and penetrated the earth very superficially, and that their leaves were of a peculiar tint of green. When in Rome he paid a visit to the Pope's alum works at Puzzeoli, where he noticed with his quick, observant eye that the earth and trees presented the same remarkable features as those on his Guisborough estate, and he immediately came to the conclusion that his land was impregnated with alum. He hastened back to England to test his hypothesis, which he soon verified by experiment, and saw that a mine of wealth lay beneath his feet. But how to work and prepare it he knew not, and there was no one in England who did, and scarcely any one in Europe, outside of Italy, which then had a monopoly of alum, and he set his wits to work to devise some means for separating it from the earth, and preparing it as a manufactured commodity for the market. Alum is a mineral salt found in clay and other earths, and is a valuable commodity used in various manufactures, and for other purposes. It was first extracted from the earth in which it was embedded, and prepared for use in the East, chiefly at Edessa, in Syria; afterwards near Constantinople; and, on the fall of the Eastern Empire, the alum workers transferred the industry to Italy where it was established in various places, and was confined to the Peninsula for more than a century, after which it spread into Germany, France, and Flanders. The Popes had works at Rome and Civita Vecchia, and carefully guarded their secret, not allowing the workmen to leave the country on any pretence whatever, under pain of excommunication, as the profits of the sale brought a handsome revenue to their coffers.