The Seashell on the Mountaintop

Been reading a lot lately and just finished off another book that's been on my to-read list for some time.  The Seashell on the Mountaintop: A Story of Science, Sainthood, and the Humble Genius Who Discovered a New History of the Earth by Alan Cutler (2003) is the story of Nicolaus Steno (1638-1686) a figure familiar to every geologist.

Steno was a bona fide genius, a Danish anatomist noted throughout Europe for his dissection skills.  His real genius was in the fact that he didn't trust what "experts" said or had written about something, he investigated everything himself.  He was invited to join the Accademia del Cimento (Academy of Experiment) in Florence, Italy where he spent a number of years working with other Italian scientists.

While there, he had the opportunity to dissect the head of a huge shark caught by fishermen in nearby Livorno on the coast and noticed that the shark's teeth looked exactly like glossopetrae or "tongue stones" found preserved in rocks.  To us today, it's an obvious conclusion that glossopetrae were fossil shark teeth but, in the 17th century, the concept that fossils are the remains of once-living organisms was highly controversial.  Many still believed the ancient claims that fossils were objects which "grew" in the rocks and any resemblance to once-living things was simply coincidence.

Steno's new-found interest in fossils led him to study sedimentary rocks in the surrounding countryside which resulted in the writing of De solido intra solidum naturaliter contento dissertationis prodromus or Preliminary discourse to a dissertation on a solid body naturally contained within a solid in 1669.  He developed a number of concepts as a result of this study which sound quite simple but actually have profound consequences by allowing us to work out the relative ages of rock strata.  These principles are:

1.  Original horizontality - the idea that sedimentary strata are originally deposited in horizontal layers.  If they are no longer horizontal, something later has disturbed them (e.g. folding during mountain building).

2.  Superposition - the idea that in a sequence of layered sedimentary rocks, the oldest rocks are found near the bottom of the sequence and the youngest near the top.

3.  Lateral continuity - the idea that sedimentary rocks extend laterally as a unit.  This allows us, for example, to match up rock units from one side of a valley to the other by assuming they were once laterally continuous.

4.  Cross-cutting relationships - the idea that if a rock unit is cut by something (e.g. an igneous intrusion, a faulty, etc.), the structure cutting through is younger than the object doing the cutting.

Steno's principles would allow you to say that A, B, C, D, E, and F formed in that order in the hypothetical area shown above.  Steno is sometimes known as the father of stratigraphy for this work (stratigraphy is the branch of geology dealing with layered sedimentary rocks).

Steno remembered by mineralogists as well for developing the law of constancy of interfacial angles - the idea that the angles between crystal faces for a given mineral, like quartz, are always constant.

One interesting thing about Steno's life is that he had a religious experience and converted from Protestantism to Catholocism while in Italy.  He was ordained as a priest and soon became a bishop and gave up his scientific investigations (a real loss to science).  He became a bit of an ascetic, didn't dress well, fasted frequently, and died an early death from some type of stomach ailment at age 48.  A sad end to a brilliant life.

This book should be read by anyone interested in geology.