Travels

FRIDAY, JANUARY 10, 2014

A Geologist's Visit to Siccar Point

Introduction

There are many important geological pilgrimage sites but few as important as Siccar Point, located along the east coast of Scotland as depicted below. James Hutton (June 14, 1726 to March 26, 1797) saw this site and stated that it was like looking into the abyss of time. "The result, therefore, of this physical enquiry," Hutton concluded, "is that we find no vestige of a beginning, no prospect of an end." Hutton's understanding of the age of the earth flew directly into the face of the general and widely held belief that the earth was only 6000 years old as calculated by Archbishop Usher (1581-1656), Primate of all Ireland. Using the Book of Genesis, Usher calculated the exact date to be at sunset on October the 22nd, 4004 BC. He was very meticulous in his calculation and so his age of the Earth was widely accepted at the time.

Location map of Siccar Point.

Hutton had major problems with this age. Based on the observations that he made around the British Isles, that was simply too little time. James Hutton, a gentleman farmer and former physician, spend over 20 years observing modern geologic processes and the results of ancient processes as can be seen in rock. His study was so full of fossils and chemical apparatus that there was little place to sit! His understanding of the time it takes for certain processes such as weathering, erosion, and sedimentation, lead him to believe that the Earth had to be many millions of years old. He saw markings and organisms in rocks that matched or were similar to markings and organisms that he saw in modern time. As a result, he came up with the idea of uniformitarianism: the assumption that the same natural laws and processes that operate in the universe now, have always operated in the universe and that all geologic phenomena may be explained as the result of existing forces having operated uniformly from the origin of the earth to the present time. It is the concept that "the present is the key to the past." Uniformitarianism in its strictest form also holds that these processes are functioning at the same rates throughout time. Modern geologists do not take such a strict interpretation; rather, they accept that geology has occurred across deep time and that many of the processes occurring today occurred in the same way in the past but not always at the same rate. Sometimes, the term actualism is used instead of uniformitarianism to reflect this modern interpretation.

The opposite of uniformitatrianism is catastrophism: the doctrine that major changes in the Earth's crust result from catastrophes rather than evolutionary processes such as erosion and tectonic uplift. Modern geologists conceede that there are catostrophic events in geology. We can quite easily list them: floods (sometimes great ones like the one that may have carved out the scablands in the west), earthquakes, volcanic erutions, landslides, etc. But, most of the processes that affect the Earth are agonizingly slow as mentioned above.

Traveling to Siccar Point

We stayed at a caravan park in Berwick-Upon-Tweed in England just south of the Scottish border. From there we traveled up the A1 toward Cockburnspath in Scotland.

Go right onto the A1107 toward the vegetable processing plant. Go left onto the unnamed road and that will take you to the Siccar Point trail head.

From the trailhead you will walk up the hill, past the ruins of St. Helen's Chapel, Old Cambus, a 12th to 15th century church, to the fence at the top of the hill.

Heading out

This is the gate at the trailhead to Siccar Point. I was surprised to see that the interpretive signs were placed by Texas Christian University!

Close up of the sign from the above photo.

Ruins of St. Helen's Church. The surviving remains of this 12th century church show that it was extensively rebuilt in the late 14th or 15th century. This church was the church of the former parish of Aldcambus and probably fell into ruin when that parish was united with the parish of Cockburnspath before 1750.

The walk toward Siccar Point.

Interpretive sign at the top of the hill above Siccar Point.

Heading down!

Hutton's Unconformity! An angular unconformity formed by the nearly vertical beds of the Silurian graywacke (425 Ma) below and the tilted Devonian Old Red Sandstone (350 Ma) above. Because of the paleotopography, sometimes the graywacke beds are higher than the Old Red Sandstone as the sandstone had filled in low spots in the paleosurface. The bumpy surface in the foreground is the basal conglomerate.

Here Tim is checking out the contact. He is standing on the Old Red Sandstone.

The sharp contact between the graywacke and red sandstone in a cliff face to the east of the famous locality. This contact is higher than the contact on the wavecut platform from the previous photo suggesting the site had significant topography at the beginning of the deposition of the Old Red Sandstone.

Here is a close up of the contact in the cliff face. There are pebbles and cobbles visible at the base of the sandstone.

This is the basal conglomerate as seen in the wavecut platform. This basal conglomerate indiates that the graywacke was exposed at the suface and subjected to weathering and erosion before the sandstone was deposited on top. The 20 pence coin is show for scale.

Here is a view of the basal conglomerate at the contact between the red sandstone above and the graywacke below.

Paleotopography is evident in these two photos to the west of the wavecut platform. The conglomerate may actually be in a channel that is now the wavecut platform. That would explain why there are fewer pebbles and cobbles in the cliffs above the platform.

This photo shows that the graywacke is actually interbedded sand and mud in this photo. Tim's foot is for scale on these vertical beds.

After a fun time of exploring Siccar Point, it was time to head back up the very steep slope. There are actually rough stairs worn into the hillside from the many people who have come to visit this geologically important site.

Here I am back up at the top. Tired but happy. That was quite a hike and quite a site to see!

Explanation of the formation of the unconformity

What makes this site so important is that it really exemplifies deep time. The Silurian graywacke was deposited in the deep ocean. It was buried, lithified, folded, uplifted, weathered, and eroded. Later, when the rock was exposed at the surface, a sea flooded the site and the red sandstone was deposited on top of the graywacke. This sandstone was buried, lithified, tilted, uplifted, weathered, and eroded so that it appears as it does today. Knowing how long it takes to do all of the above tasks, this site represents a truly immense time in human terms. Geologically 80 million years, 345 million years or even 425 million years are not all that long considering the earth is 4.6 billion years old. But to us, 10,000 years seems like a very long time ago; therefore, we must switch our minds to a deep time scale to work on geological projects because the time is just that immense.

Figure by Chris Rowan

A pilgramage to Siccar Point is a must for all geologists. It is fascinating to walk in the footsteps of the pioneers of geology. How incredibly insightful and creative they were to work out what no one had ever attempted before. There was no previous research to guide them, no background information. They had only their observations and their imaginations to work out the complex interpretations that now seem so obvious to us. Perhaps one day, long into the future, people will look back on the research being conducted today and wonder at our ignorance. I can only imagine what they will understand.