Directions for inquiries concerning stones and other materials for the use of building; together with a suggestion for retriving the art of hardning and tempering steel for cutting porphyre and other hard marbles

1. To observe the great difference in the degrees of hardness in Free-stones, together with the other qualities to be found in them, and to inquire into their Causes: There being (e. g.) a sort of gray Free-stone atparis every where on the South-side of the Riversene , which is of a reasonable course greet, and so soft when first taken out of the Quarry, that ’tis drest and hewn with broad sharp Axes almost as easily as dried Clay; but grows harder and harder in the Air very durable and exceeding fit for building.