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by Peter Dryburgh Nicolaus Steno is perhaps best known in connection with the crystallographic law which states that the angle between two faces of a crystal is the same as the angle between the two corresponding faces of any other crystal of the same substance. Indeed, some text-books refer to this law as Steno's Law. What is much less widely appreciated is Steno's enormous contribution to the establishment of the whole science of geology. In order to understand his involvement in geology, it is helpful to know something of his background and the reasons for his international standing as a scientist, which arose initially from his work as an anatomist. Steno's early life and student days Although he is known universally by the latinized version of his name, Nicolaus Steno, he was born in Copenhagen in January 1638 and named Niels Stensen. His father, Sten Pedersen, was a prosperous goldsmith and lapidary who died in 1644, after which Steno's brother-in-law, Jörgen Carstensen, was appointed his guardian. After Pedersen's death, his workshop was taken over by his daughter's husband, Jakob Kitzerow, although Steno stayed on in his mother's house and was sent to the Metropolitan School when he was about ten. During his schooldays, he developed a love of mathematics and it is clear also that he was so familiar with metalworking, lens polishing and instruments that a biographical note by Scherz states that 'the workshop was undoubtedly the boyís first school.' During the eight years for which Steno attended the grammar school, a quarter of the population of Copenhagen perished in an epidemic but, ironically, this early part of the seventeenth century was a period when the study of medicine was flourishing in Denmark. Upon leaving school in 1656, Steno matriculated in the University of Copenhagen to study anatomy and medicine. His tutor was the great anatomist Thomas Bartholin, a member of the family which dominated academic life in Denmark for three generations and included Erasmus Bartholin, who discovered double refraction in calcite in 1669. Academic life was severely disrupted in 1667 by the war with Sweden but Steno pursued his studies with diligence and intense concentration. The 'Chaos Manuscript', found in a library in Florence in the nineteen-fifties, consists of ninety pages of Steno's own notes from his time at the University of Copenhagen. There are detailed comments about his many experiments in different fields of study and his reflections on Christianity and philosophy. There are copious notes from a huge variety of sources and descriptions of the construction of different instruments and of chemical and metallurgical experiments. Of particular interest in a geological context, are his reflections on the problems of geomorphology and his emphatic declaration of the importance of practical observation. In the autumn of 1659, Steno left Copenhagen, which was still under siege, and travelled through northern Germany to Amsterdam on the first stage of his academic tour. It was during his first year in Amsterdam that he discovered the parotid salivary duct still known as the ductus Stenonianus and started his detailed study of the chemistry and physics of hot-springs. By 1660 he had moved on to Leiden and, after matriculating at the University, he commenced his extensive research into glands, muscles and comparative anatomy, one of his fellow students being the Scottish naturalist Sir Robert Sibbald. In 1664, before obtaining his doctorate, he returned to Copenhagen following the death of his mother's fourth husband and was in great hope of being offered a university post. However, university politics and nepotism prevailed, so the post was given to a man who had produced no original work and was in all respects Steno's academic inferior but was related to an influential professor. Steno then collected together all his anatomical work in a treatise, which he dedicated to the king of Denmark with a plea for help but, when another university post became available, he was again passed over. His mother died later in the year and he left Copenhagen to visit Paris and Montpellier. In December 1664, the University of Leiden conferred on him the degree of Doctor of Medicine. When he received the news of this honour, he was already in Paris where he associated with all the most distinguished scholars of the day and carried out important research into embryology and the anatomy of the brain. At this time, the theory of Descartes concerning brain function was widely accepted. Although an eminent mathematician and philosopher, Descartes had little knowledge of practical anatomy or physiology and one of the cornerstones of his theory was the unique occurrence of the pineal gland in the human brain. In a famous lecture, Steno showed that the pineal body existed in all the animals he had dissected and so disproved the theory. This refutation of the Cartesian theory greatly enhanced Steno's reputation, and it was published some years later (1669). Steno left Paris in 1665 to go to Montpellier, at that time a major centre of intellectual activity. It was there that he came into contact with such English scientists as Martin Lister and John Ray and became acquainted indirectly with other members of the Royal Society and their activities. Early in 1666, Steno left France for Italy and was received in Pisa at the winter residence of the Medicis by Grand Duke Ferdinand II of Tuscany, an enthusiastic patron of the arts and sciences. Ferdinand encouraged him to pursue his research and provided him with generous support and assistance, which continued when he moved on to Florence. In 1666, Steno had reached the age of 28 and had an international reputation as an anatomist and zoologist but two momentous events occurred in that year, one of which turned his attention to the systematic study of geology and another which changed the entire direction of his later life even more radically. The first event was the chance landing near Lavorno of a great white shark (Carcharodon rondeletti) by fishermen, and the second was his conversion to Roman Catholicism. The giant shark was such an unusual specimen that the Grand Duke ordered the head to be transported to Florence for Steno's anatomical studies. The resulting dissection and analysis were carried out with the thoroughness for which Steno was renowned and his acute powers of observation and meticulous recording provided a mass of new information on functional anatomy.The report of the dissection was appended to his important treatise on muscles, Elementorum Myologiae Specimen, published in 1667.The feature of greatest interest from a geological point of view is Steno's extensive digression on sedimentation and fossilisation. The birth of palaeontology The need to include a geological digression in an anatomical treatise arose from Steno's controversial comparison of the shark's teeth with the tonguestones (glossopetrae) which were commonly found in Malta and other places. Although fossils had been found and discussed for centuries, there was no general support for the idea that they were preserved relics of living creatures. After painstaking examination of the shark's teeth, Steno listed eleven observations and six conjectures and with cautious but relentless logic established beyond doubt that the glossopetrae had indeed been sharks' teeth and that accompanying mollusc shells were the remains of formerly living creatures. His discussion of sedimentation processes reveals also an appreciation of the cyclic nature of erosion and deposition. His style of expression was free from dogmatic assertion and he concluded: Nothing seems to contradict the theory that the bodies excavated from the earth and which resemble parts of animals must also have been parts of animals.This simple statement, following the first unequivocal proof of the nature of fossils, may be seen as heralding the birth of palaeontology. In an address to the British Association in 1881, Thomas Huxley acknowledged some of the earliest work on the organic origin of fossils but stated that the true interpretation of fossils was stated in a manner that left nothing to be desired in the latter half of the seventeenth century. The person who rendered this good service to palaeontology was Nicolaus Steno. Steno's religious conversion and the 'Prodromus' After many years of religious reflection and theological study, Steno decided finally to embrace Catholicism and was formally received into the Church in 1667. On the same day, he received a communication from King Frederik III of Denmark asking him to return to Copenhagen and offering him an annual pension. He hesitated to accept the offer, probably because he was unsure about the effect his conversion might have upon it: Denmark was a strictly Lutheran country at this time. The Grand Duke had approved of an extensive programme of work proposed by Steno and agreed to support him. As a result, much of the year 1667-68 was spent in geological excursions and travels, especially in Tuscany, and Steno visited mines and quarries and studied the sedimentary rocks of Elba. At the end of 1668 he abruptly gave up his rooms in Florence and started upon a long and circuitous journey back to Copenhagen. The reason for his unexpected departure is unknown but may have been the result of discrete pressure by King Frederik. Whatever the reason for his leaving Florence, he acknowledged that he would be unable to complete the agreed programme of research so, largely in the spirit of an apology, he decided to write for the Duke an outline or extended synopsis of the major treatise which he had originally intended to write. This publication, entitled 'De Solido Intra Solidum Naturaliter Contento Dissertationis Prodromus' (The Prodromus to a Dissertation Concerning a Solid Enclosed by Process of Nature Within a Solid) appeared in 1669. The Prodromus, as it is usually called, is one of the most amazing works in the history of geology and foreshadows many aspects of the subject that did not become established until more than a century after its publication. The book's rather obscure title gives no inkling of the wealth of ideas and observations which it contains. Under the general heading of 'solids contained within solids', Steno includes fossils, agates and crystals in rocks and also the strata which form the earth's crust in Tuscany: a typical bed lies between higher and lower beds and so may be regarded as enclosed. No summary of the Prodromus can convey the concentrated brilliance of the work and Steno's style of writing is so precise and economical that it is difficult to summarise without significant loss. There are few superfluous words. Steno never indulged in the unsupported speculation so common amongst his contemporaries but went into the country to study the rocks themselves and deserves to be regarded as the first field geologist. The outline of selected topics which follows is given in an attempt to convey the breadth and importance of this monumental work. The geological content of the Prodromus The Prodromus is formally dedicated to The Most Serene Grand Duke (Ferdinand II) and the introductory preamble reveals much of Steno's attitude to geological investigation. After a detailed apology for failing to complete all the work planned, Steno outlines the four parts of the proposed dissertation and discusses some general principles, the first of which defines a general problem: Given a substance endowed with a certain shape, and produced according to the laws of nature, to find in the substance itself clues disclosing the place and manner of its production.Later in the introduction he observes: There seem to me two main reasons underlying the fact that in the solution of natural problems not only are many doubts left undecided but also most often the doubts multiply with the number of writers.In the main text, Steno extends his original proof of the origin of fossils and extends it to include plant remains. He observes that all strata were deposited originally from a fluid medium subject to the effects of gravity and enunciates three principles of stratigraphy. First, in any vertical sequence of beds, the oldest bed must be at the bottom and the youngest at the top (principle of superposition). Second, from the observation that sediments were deposited from a fluid, all beds must have been originally horizontal, so inclined beds must have been tilted after their consolidation (principle of original horizontality) and third, horizontal beds would have extended in all directions, so similar beds separated by a valley must have been originally continuous (principle of original lateral continuity). In the following text he distinguishes between
marine and fluviatile beds and, in discussing the origin of mountains,
shows that they do not grow like trees but classifies them as block or
fault mountains, volcanic mountains, mountains of erosion and folded mountains.
He points out that sedimentary and volcanic rocks are different because
they are produced by different processes.
1. Rocky strata are whole.
As well as being the first recorded use of stratigraphical sections, Steno's diagrams and their explanatory notes reveal a huge extension of the accepted timescale and an appreciation of the continuity of geological processes. Steno discusses the origins of ores and gems and shows that crystals grow by accretion of fresh material onto the existing planes from outside and not, as many writers then supposed, by organically growing like plants from within. By considering various irregular basal sections of quartz crystals, he established that the interfacial angles were constant. (Although Steno made no claim to the generality of this law, it is always attributed to him. The concept of a crystal as a type of solid was introduced by Höttinger in 1698 but in Steno's time, the word referred exclusively to quartz. It was not until after the invention of the contact goniometer in 1780 and the comprehensive measurements made by de L'Isle that the constancy of interfacial angles was established as a general law). The text of the Prodromus sparkles with insights and ideas of astonishing originality but everything is based upon careful and critical observation. To anyone interested in the history of science, particularly of geology, this is a fascinating work. In view of the fact that it was only a hastily composed, preliminary synopsis of the intended treatise, it is probably fair to suggest that the completion of the full work might have advanced the development of geology by at least a hundred years. Steno's travels and work after the Prodromus (1668-1671) As soon as he had arranged for the printing of the Prodromus, Steno embarked upon the long journey back to Denmark. His route was far from direct and he travelled extensively in Italy, Austria, Hungary, Bohemia and Germany, studying geology and amassing a large collection of specimens. He arrived in Amsterdam in 1670 and learned of the death of King Frederik, which was followed quickly by news of Grand Duke Ferdinandís serious illness. These sad events caused him to abandon his journey to Copenhagen and return to Florence but, before he arrived, Ferdinand was already dead. Fortunately, Ferdinand's successor, Cosimo III, gave Steno the same level of enthusiastic support as had his father and provided him with a house beside the Arno and apartments in the Palazzo Medici. With Cosimo's permission Steno did no scientific work for six months but occupied himself in writing a theological treatise. In the summer of 1671, he studied various grottos in the Alps and showed that the ice inside them was not caused by the contrasting summer heat outside, so refuting the popular but superficial Aristotelian theory of 'antiperistasis'. He reported his findings to the Grand Duke in two letters which were effectively his last geological writings. For the second time in his life, he received a royal invitation from Copenhagen - this time from King Christian V - and arrived there in 1672 to teach and study anatomy once again but was not allowed to become a professor because the Lutheran orthodoxy demanded religious conformity. The restrictions on his work caused by religious intolerance soon made his position miserable and, having obtained permission from the King, he returned to Florence in 1674 to take up the position of tutor to the Medici court. In the following year he became a priest and, for the rest of his life, his dedication to religion displaced all other interests. He became a bishop in 1677 and died in Schwerin in 1686, admired and respected throughout Europe for his piety, intelligence and honesty. Cosimo III had his coffin transported to the crypt of the Medici church in Florence, San Lorenzo. Steno's Indice One of his last tasks before leaving the study of geology had been the preparation of a detailed catalogue of the Medici collection of minerals and related items, supplemented considerably by the addition of his own collections, gathered during his extensive travels. This catalogue is known as 'Steno's Indice' and is a model of meticulous recording. The specimens are divided roughly into numbered groups; 1-29 quartz crystals; 30-92 emeralds, diamonds and ores; 93-114 pyrites and other minerals; 115-216 marine stones, mussels, snails, fossils etc.; 217-258 corals; 259-304 earth and rock specimens, volcanic products, ores etc. This large collection is now mostly lost and can be assessed only by Steno's description but it has been observed that it was a collection specifically for the purposes of geological research and not merely a random collection of curios. Professor R. Spärck noted in 1956: It thus seems to me that this Steno collection has been composed for a quite special purpose of research, which can very seldom be said about contemporary collections, if there is any example of this kind at all.It is consistent with everything that Steno did that, even in assembling a collection, he contributed something new and original to geology. Epilogue After Steno's death, his work fell into obscurity and was not rediscovered until late in the nineteenth century. In 1881, the Second International Congress of Geologists in Bologna laid a wreath on Steno's grave and erected a marble plaque to his honour in the cloisters of San Lorenzo. In the second half of the twentieth century, scholars such as Gustav Scherz have explored the work of this extraordinary man and a symposium on Steno and brain research in the seventeenth century was held in Copenhagen in 1965. An important result of this symposium was the bringing together of research workers who recognised the international importance of Steno and decided to publish a complete edition of his geological works. This appeared in 1969 and is referred to in the list of further reading given below. Further Reading: Eyles, V.A. 1954. Nicolaus Steno, Seventeenth-century Anatomist, Geologist & Ecclesiastic. Nature, Volume 174, pp. 8-1 Garboe, A. 1958. The Earliest Geological Treatise by Nicolaus Steno (1667), Macmillan & Co. London. Sherz, G. (ed.), 1958. Nicolaus Steno and his Indice, Acta Historica Scientiarum Naturalium et Medicinalium, Volume.15, Munksgaard, Copenhagen. Sherz, G. (ed.), 1969. Steno Geological Papers, ibid , Volume 20, Odense University Press, Odense. Sherz, G. (ed.), 1971. Dissertations on Steno
as Geologist, ibid, Volume 23, Odense University Press, Odense.
Peter Dryburgh is a physical chemist by profession but has always had an interest in earth science and its history. He retired from the University of Edinburgh, where he was a lecturer in the Electrical Engineering Department a couple of years ago and is currently the President of the Edinburgh Geological Society.
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