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 was nothing but metaphysical speculation. Contrary to many other works of the 17th century, it had an impact on contemporary scientists through three Latin editions and its translation into English by Henry Oldenburg in 1671.
The Prodromusis divided into four parts. The first contains an investigation on the origin of fossils. The second part analyzes the following fundamental problem: "given a substance having a certain shape, and formed according to the laws of nature, how to find in the substance itself evidences disclosing the place and manner of its production." The third part discusses different solids contained within a solid in relation to the laws discovered and presented in the previous part. This is the section dealing mostly with crystallography. The fourth part is largely a consideration of the geological changes which Steno was able to interpret from his observations throughout Tuscany.
A fundamental part of Prodromus concerns the aspects and the mechanism of the growth of crystals, which are also solids within solids. In that respect Steno discovered the fundamental law of crystallography known as the "law of constancy of interfacial angles," which states that regardless of the variations in shape or size of the faces of a crystal, the interfacial angles remain constant. At the end of Prodromus, Steno in a series of diagrams illustrates the geological history of Tuscany. These sections, the earliest of their type ever prepared, fully substantiate the claim that Steno is one of the founders of stratigraphy and historical geology and perhaps the first geologist in the modern sense.
Steno, in his general concept of the universe, adopted the doctrine of the four Aristotelian elements: fire, earth, air, and water. However, his concept of matter was Cartesian, since he considered a natural body as an aggregate of imperceptible particles subject to the action of forces as generated by a magnet, fire, and sometimes light.
In paleontology, Steno clearly understood the organic origin of fossils and their importance as indicators of different environments of deposition. Assuming that strata had been deposited in the form of sediments from turbid waters under the action of gravity, Steno established some of the fundamental principles of stratigraphy: deposition of each bed upon a solid substratum, superposition of younger strata over older ones, and occurrence of all beds except the basal one between two essentially horizontal planes. In structural geology, Steno visualized three types of mountains: mountains formed by faults, mountains due to the effects of erosion by running waters, and volcanic mountains formed by eruptions of subterranean fires.
In 1672 Steno became professor of anatomy in Copenhagen. As a Catholic, he encountered so much religious intolerance from the Protestant community that he returned to Florence, where he was put in charge of the education of Cosimo III, the son of the Grand Duke. In 1675 Steno took Holy Orders, and a year later Pope Innocent XI appointed him bishop of Titopolis and apostolic vicar of northern Germany and Scandinavia. He died in Schwerin on Nov. 26, 1686.
The most comprehensive biography of Steno, including the translation of all his geological works, is in Steno: Geological Papers, edited by Gustav Scherz and translated by Alex J. Pollock (1969). Some biographical information on Steno is in Gustav Scherz, ed., Historical Symposium on Nicolaus Steno (1965). Other accounts of his life and contributions to geology are in Sir Archibald Geikie, The Founders of Geology (1897); Karl von Zittel, History of Geology and Palaeontology (1901); and Frank D. Adams, The Birth and Development of the Geological Sciences (1938).
Moe, Harald, Nicolaus Steno: an illustrated biography: his tireless pursuit of knowledge, his genius, his quest for the absolute, Copenhagen: Rhodos, 1994.
Scherz, Gustav, Niels Steensen (Nicolaus Steno), 1638-1686: the goldsmith's son from Copenhagen who won world fame as a pioneering natural scientist but who sacrificed science to become a celebrated servant of God, Copenhagen: Royal Danish Ministry of Foreign Affairs, 1988.