The Danish naturalist Nicolaus Steno (1638-1686) established the law of superposition and the law of constancy of interfacial angles.

Nicolaus Steno, originally Niels Stensen, the son of a goldsmith, was born in Copenhagen on Jan. 10, 1638. He entered the University of Copenhagen in 1656 to begin studies in medicine which he continued in Amsterdam and Leiden. After studying anatomy in Paris in 1664, he went to Florence in 1665. He became court physician to the Grand Duke of Tuscany, Ferdinand II, who subsidized Steno's scientific interests.

During this period Steno investigated the geology of Tuscany with its related mineralogical and paleontological problems. His De solido intra solidum naturaliter contento dissertationis prodromus (1669; Introduction to a Dissertation concerning a Solid Body Enclosed by Process of Nature within a Solid) was one of the most fundamental contributions to geology because of Steno's qualities of observation, analysis, and inductive reasoning at a time when scientific research...