Abstract Ole Worm, Professor of Medicine at Copenhagen University 1624–1654, collected natural objects and artefacts with a view to letting students learn through observation and the touch of real things. Among the objects were fossils. Through Worm’s correspondence from 1607 to 1654, his growing understanding of petrifaction and petrifactions (fossilization and fossils) and its circumstantial background in the Nordic Renaissance has been investigated. Worm studied medicine with anatomy, botany and (iatro)chemistry at European universities. He began as Professor Pædagogicus and practising physician in Copenhagen in 1613 and he pursued interests in botany and in Nordic philology supported by King Christian IV. Objects for demonstrative instruction were obtained through his correspondents and were arranged systematically in Worm’s museum. The first fossils were identified chemically as petrified mollusc shells and wood, but without attention to species and original environment. With limited zoological knowledge and little field experience, but well trained in anatomical observation and description, and well read, Worm developed his understanding of fossils. He compared sharks’ teeth and glossopetrae , adding evidence to former comparisons. Christian orthodoxy was a barrier to geological and evolutionary thinking. Worm rejected superstition and prepared the way for the scientific comprehension of fossils in the Nordic cultural sphere.

Silicified stumps preserved within a late Eocene lahar deposit have diverse mineralogy, ranging from opal-CT to chalcedony. In specimens that contain both silica polymorphs, the minerals appear to have originated independently, rather than from diagenetic transformation of an opaline parent material. This petrifaction process is unlike the progressive transformation of opal-A→opal-CT→chalcedony that has long been accepted as a general model for wood silicification. At the Florissant fossil forest, petrifaction occurred in several stages, beginning with precipitation of amorphous silica on cell wall surfaces. Cell lumina later became filled with opal-CT and chalcedony. A final phase of silica deposition is evidenced by chalcedony-filled fractures that crosscut permineralized tissues in some specimens. Spaces between adjacent tracheids commonly remain unmineralized, causing the silicified wood to remain permeable to water, and to readily cleave radially and tangentially. To a lesser degree, the fossilized wood is subject to transverse fracturing. This combination of structural characteristics causes Florissant fossil stumps to be susceptible to damage from freeze-thaw weathering.

It has been suggested that Robert Hooke had some influence upon Nicholas Steno’s forming geotheory, but decisive evidence has not yet been given. To reconsider the Hooke–Steno relationship, this paper examines Boyle–Steno relations by not only comparing their texts but by assessing a mediating role played by Ole Borch. In investigating the origin of the Stenonian terminology “solids within solids” in his Prodromus (1669), I shall point to two possible sources. One is represented in Steno’s first dissertation De thermis (1660), which was composed under the influence not only of scholastic themes but also of physiological textbooks of the age. The other is Robert Boyle’s texts on petrifaction and mineralogy written in the 1650s and 1660s, which appeared in part in 1661 and 1672, and which were ultimately published in 2000. A similar terminology for the relations of fluid/solid bodies is also observed in Hooke’s first dissertation on capillary action (1661), Attempt for the Explication of the Phaenomena , apparently deduced from the Boylean concept of fluidity and firmness. On the other hand, Steno’s mentor Borch met Boyle in 1663 during his journey through Europe, and it is likely he transmitted Boyle’s idea to Steno, though Steno himself made no reference to Boyle by name. The fact that Boyle’s works were a possible common source for Hookian and Stenonian geoscientific thought leads us to reconsider Boyle’s contribution to the history of early modern geotheory.