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

Abstract

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 at paris every where on the South-side of the River sene , 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.