A geologic pilgrimage: Edinburgh, Scotland--The Enlightenment and James Hutton

This blog is broadly about fluid mechanics in geology, and eventually I’ll get to fluids in this post! But, along the way...some early history of geology, and a pilgrimage to honor James Hutton, the discoverer of 'deep time.'

This is the section of Grayfriars where Hutton is buried, the
plaque shown below is  the white rectangle in the middle left.
Photos in this post by G. Lopez

From 1730 to about 1790, Edinburgh, Scotland, enjoyed a period of incredible intellectual focus and productivity, the "Scottish Enlightenment." For an excellent overview how our modern concepts of time evolved and the four instrumental scientists in this evolution (Copernicus, Galileo, Hutton, and Darwin), see Jack Repchek's book "The Man who Found Time: James Hutton and the Discovery of the Earth's Antiquity," particularly the Prologue.



During Hutton's time in Edinburgh, industry, commerce, agriculture, science, and the arts flourished.  David Hume (philosopher, historian), Adam Smith (economist), and Joseph Black (chemist) prospered during this time. And, it was here in Edinburgh that the landowner, farmer, agriculturalist, physician, and natural philosopher, Hutton, founded our modern science of geology.  


Why was Hutton so important? At the time of Hutton, many natural scientists believed that all rocks were formed underwater, the so-called "Neptunist" school of thought, championed by Abraham Gottlob Werner. Hutton’s ideas about the evolution of the earth required long times, the so-called “deep time” popularized by John McPhee in 1980.   He also introduced and rigorously pursued the idea of “falsification” of ideas in science: that conjectures should be posed in a way that leads to verifiable predictions, and in a way that can be tested as false. Without Hutton’s work, Darwin’s work in the next century would have been impossible. In fact, Hutton had recognized natural selection as a “beautiful contrivance”, more than a half century before Darwin. 


For a geologist like myself, a visit Edinburgh feels rather like a pilgrimage, especially when undertaken on Easter Weekend! Here, nearly in the midst of Edinburgh and all within walking distance, are three sites of special interest--Hutton's "section," Hutton's "rock," and Hutton's grave. Locating and getting to these sites, however, turned out to not be trivial task.

Trips to geologic sites of interest do not always go as planned. Guidebooks may be outdated, outcrops can be altered by quarrying activities or just normal weathering. A few years ago, my husband and I were in southern Germany and I was trying to collect some rocks brought up from deep in the crust ("xenoliths") during volcanic eruptions by visiting various rock quarries. I had, in accord with the Geologic Code of Conduct, successfully contacted some quarry owners in advance, but couldn't get hold of one at the most important site. I was resigned to the fact that I might visit, but not collect, at that one if I could even find it. Nevertheless, photos of that quarry would be helpful in my research. We searched and searched but couldn’t find that quarry (we were working from an old guidebook and the quarry may have been closed). We had, however, found several quarries that were good, but nothing like the superb and elusive one that we were searching for.  Finally, toward the end of the day, my patient husband said "Do you want to keep searching for El Dorado? Or, go back to the sites we already found." Since that day, "El Dorado" has had a special meaning for us--the goal of a search that is not going well. On this 4-day trip to Edinburgh, it turned out that there were three El Dorados--the grave, the section, and the rock!

According to one source (*McIntyre and McKirdy, p. 45) Hutton’s grave was unmarked for 150 years after his death in 1797, at the age of 71, and he was buried in an “obscure plot” in what is now known as Grayfriars Kirkyard and cemetery. We began our quest by walking there on a drizzly Scottish day. (Grayfriars is more famous for the dog, Bobby, that guarded his master’s grave for 16 years than for being the site of Hutton’s grave, and tourists flock to see the dog, who occupies front and center of the entrance!) There we found gravestones dating back to the 1600's, but alas, no clue about how to find Hutton.  Finally, on our way out of the churchyard, we discovered the index map, and also discovered that the grave was behind a locked gate. Failure...El Dorado #1. 

The only sign in the vicinity of Hutton's section and
Hutton's rock! 

Then, we walked about a mile toward a visitor center that lies at the base of two very famous geologic features in Edinburgh--Salisbury Crags, and Arthur's Seat. Somewhere up there lay Eldorado’s #2 and #3. The climb up these features seemed intimidating!

The next day, we started over, revisiting Greyfriars church, where we found a most helpful volunteer, Wally, who eagerly produced a key and walked with us to unlock the gate. There, somewhat weedy and overgrown, was indeed Hutton’s grave with a plaque on the wall above it (the two photos above).  On the stroll back to the church, I naively asked whether this was an Anglican church—big mistake! Need to do my history work when I get back hom3! Church of Scotland!!

We then hopped a bus back to the visitor center for Holyrood Park and, with our guidebook, found the “Volunteers' Walk,” a great path up into the saddle between Salisbury Crags and Arthur's seat. These two features are the most spectacular of several volcanic dykes and sills that were intruded into the ancient sedimentary rocks in this area.  Hills on the skyline in Edinburgh are typically underlain by volcanic materials such as these, and Edinburgh Castle famously is built on such a feature. Volunteers Walk is a fairly gentle and well groomed path up past Hunter's Bog, bringing  us to "The Hause", and El Dorado #2, Hutton's section, on the back-side (for us) of Salisbury Crags.

Fluid dynamics alert!! At Hutton’s section, a volcanic magma rising toward the surface was trapped between beds of the sandstones in the area forming a feature called a “sill.” Beneath this sill are well-bedded sediments of the Cementstone Group, vaguely red and white in color but heavily stained on their surfaces.  At the contact between the magma and the sediments, the sedimentary rocks were “baked” by the heat of the magma as it was intruded between the layers, and the magma was chilled by the sedimentary rocks, forming a glassy “skin” about a centimeter thick. The volcanic magma has crumpled and rotated the sediments, and in places, engulfed them (photo above with deformed sediments sweeping upward).  Such deformation could not be explained by the Neptunists--those who argued at the time that all rocks were formed underwater--and this site became critical for Hutton in proving his theories.

About 100 meters further along the path here (west?)  lies a very undistinguished looking rock, Hutton’s Rock.  Although nearly impossible to see today because of the weathering and staining, Hutton recognized that the magma (a teschenite) had been extensively altered by hematite (Fe3O4), and that a vein very rich in hematite and several centimeters in thickness cuts through the rock.  He saved it from the quarrying operations and, amazingly, it has remained in place for more than two centuries (possibly because it is so undistinguished in appearance!)

Alert readers: The Geological Code of Conduct is an agreement signed by all European countries regarding visiting and preserving geological outcrops. Please read and obey.

All in all, a successful trip with El Dorado’s #1,2 and 3 all found!

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*Additional references: Lothian Geology, An Excursion Guide, A.D. McAdam and E.N.K. Clarkson, published by the Edinburgh Geological Society, 1960 and updated and reprinted in 1996.  We got this book at the Carson Clark Gallery (a map center) and the owner claims that a few years ago he bought up all few hundred copies that were still in existence!)


*James Hutton, The Founder of Modern Geology, by D.B. Mcintyre and A. McKirdy, a revised and amended addition published in 2001 by the National Museums of Scotland.