Niels Stensen and geology, 2
In 1660, Steno went to Holland in order to get a doctoral degree in medicine. Besides his discovery of ductus stenonianus, he delivered a small thesis on hot springs, ”Disputatio Physica De Thermis”, at the University of Amsterdam the same year and proceeded to the University of Leiden to complete his studies in medicine. Steno later got his doctoral degree in medicine in absentia while staying in Paris in 1664-1665.
During the summer 1665 he travelled to Montpellier in South France where he stayed during the winter. In the beginning of 1666, he went on to Tuscany in northern Italy where he was well received in Pisa by the Grand Duke Ferdinando II and his family. Pisa had a small natural history museum, Galleria de Semplici. Here, Steno would spend some time in 1668 and 1671-1672 organizing and curating the collection of minerals etc., so that it could be coordinated with the collection of minerals and fossils in Palazzo Pitti in Florence. His work would later be documented in ”Indice di Cose Naturali” which is an incomplete catalogue of the ducal natural history collection, including samples collected and curated by Steno himself.
From Pisa, Steno traveled to Florence before going on to Rome. Here, he met the Jesuit Athanasius Kircher, whose work on magnetism he had read and excerpted as a student. Kircher sought to demonstrate his many ideas in a museum, Museum Kircherianum, which held many rare items, including fossils. Steno criticized and rejected Kircher´s ideas about Earth, in particular, Kircher´s theory on the organic production of mountains.
Back in Florence, Steno devoted his time to anatomical studies. He also attended the meetings of Accademia del Cimento which took place in Palazzo Pitti. Here, he saw the collection that included minerals, fossils, (e.g. glossopetrae from Malta). He had just finished his treatise on the muscles, ”Elementorum Myologiae Specimen”, when he received the head of a big shark that had been caught off Livorno. Based on his study of the head, he wrote a paper ”Canis Charchariæ Dissectum Caput”, which was published in 1667. Steno compared the teeth of the shark with glossopetrae, and recognized the origin of these as shark teeth. Thus he reached his conclusion by applying the well-known scientific principle ”the present is the key to the past”. For illustrations he borrowed two plates from an unpublished thesis, ”Metallotheca Vaticana”, by Michaelis Mercati, on the natural history collection in the Vatican. (The picture of one of the plates demonstrates the close similarity between Mercati’s dried specimen and an old museum specimen today.) Others, however, had recognized the organic origin of fossils before Steno, e.g., Leonardo da Vinci and Fabio Colonna.
Steno then left Florence to take a closer look at the geology of the area, beginning with the city’s environs. Steno’s fieldwork would be essential to his later fame and reputation. The conclusions he reached, based on his observations of the strata in Tuscany and their fossil contents, enabled him to found the geological science of stratigraphy. His principle of superposition was later described and illustrated in ”De Solido”. We know that Steno collected many fossils, especially bivalves and gastropods, from the Tertiary-Quaternary sediments in Tuscany. He included them in the collection in Palazzo Pitti, but they were not recorded in ”Indice”, probably because there were too many.