These are the words written by John Playfair as he described an extraordinary boat journey he made with James Hutton in 1788 to Siccar Point, a spot where Hutton found confirmation of his model of the Earth's development. At the point, Silurian graywacke sandstone layers (425 million years old) stand nearly vertical, and are overlain by bright orange and brown layers of the Devonian Old Red Sandstone (345 million years). Such features are called unconformities. During the interval of time before the deposition of the Old Red Sandstone, the sea floor had been compressed and thrust upwards into a mountain range that was subsequently eroded completely away. Such events required the passage of vast amounts of time, something quite incompatible with the mere 6,000 years of Earth's existence assumed by medieval religious scholars. Hutton's explorations of Scotland ignited the revolution that led to the development of the science of geology.
In 2001 I had the chance to visit some of Hutton's most famous rock exposures. We had put together our very first international field studies journey to England and Scotland, and being unfamiliar with the territory, we had contracted with a tour company to take care of the logistics. We got a canned tour of the famous tourist localities like Stonehenge, Big Ben, and Edinburgh Castle, but we made special arrangements with the tour company (for a price) to deviate from their usual itinerary (we missed the golf courses of St. Andrews) so we could instead head into the southern uplands of Scotland to Siccar Point. We committed to the trip 1 1/2 years in advance, having no idea that hoof-and-mouth disease was about to be detected in the British Isles, including the farms around Siccar Point. To my almost unspeakable frustration, access was impossible. Not wanting to just give up, I pulled out the topo maps and we made our way to a campground on the coast about a mile north of Siccar Point. I read the passage from John Playfair to the students, and than I ran as far as I could along the beach cliffs to where I could see the point, but not the relationships (although we could pick up the associated rocks along the coast).
For years I've been showing a video to my students on the development of the theory of plate tectonics. It was done in the early 1990s but has held up well aside from the ancient computers in some of the scenes. It begins in Edinburgh with a look at the Salisbury Crags and Arthur's Seat, where James Hutton discovered an ancient volcano that once sat on the sea floor. Other observers in these early days of geology thought that basalt accumulated on the sea floor by precipitating out of the water, much like salt deposits in a drying bay. Hutton found a contact zone in a small quarry at the base of the Salisbury Crags where the intruding basaltic rock had pried up the previously existing sedimentary layers forming a vast sill. In other parts of Scotland he found intrusions of granitic rock that had done the same thing. In short, he had discovered intrusive (or plutonic) igneous rocks, and opened our eyes to an entirely different way of considering our planet, an active planet with an internal heat source, and cyclical processes that had been operating for millions, not thousands, of years.
|Hutton's resting place is on the left side of this yard.|
As we made our way down the road towards Arthur's Seat, we noticed that nearly every man on the street was wearing a formal kilt, and we wondered why. As we approached Holyrood Palace, we realized that everyone was gathering for a "garden party" hosted by Queen Elizabeth. There were just a few people in attendance, about 8,000 of them. From our vantage point on the flank of Arthur's Seat, we could pick her out, wearing a blue outfit in a receiving line next to the side of the building just slightly left of center in the picture below. Yes, it was a crazy, unique day.