BN: James Hutton

12 May 2020

May 12, 2020 Comment

Siccar Point - the world's most important geological site and the birthplace of modern geology

Siccar Point is world-famous as the most important unconformity described by James Hutton (1726-1797) in support of his world-changing ideas on the origin and age of the Earth.

James Hutton unconformity with annotations - Siccar Point

In 1788, James Hutton first discovered Siccar Point, and understood its significance. It is by far the most spectacular of several unconformities that he discovered in Scotland, and very important in helping Hutton to explain his ideas about the processes of the Earth.At Siccar Point, gently sloping strata of 370-million-year-oldFamennian LateDevonianOld RedSandstone and a basal layer of conglomerate overlie near vertical layers of 435-million-year-old lowerSilurianLlandovery Epoch greywacke, with an interval of around 65 million years.

Standing on the angular unconformity at Siccar Point (click to enlarge). Photo: Chris Rowan, 2009

As above, with annotations. Photo: Chris Rowan, 2009

Hutton used Siccar Point to demonstrate the cycle of deposition, folding, erosion and further deposition that the unconformity represents. He understood the implication of unconformities in the evidence that they provided for the enormity of geological time and the antiquity of planet Earth, in contrast to the biblical teaching of the creation of the Earth.

How the unconformity at Siccar Point formed.

At this range, it is easy to spot that the contact between the two units is sharp, but it is not completely flat. Furthermore, the lowest part of the overlying Old Red Sandstone contains fragments of rock that are considerably larger than sand; some are at least as large as your fist, and many of the fragments in this basal conglomerate are bits of the underlying Silurian greywacke. These are all signs that the greywackes were exposed at the surface, being eroded, for a considerable period of time before the Old Red Sandstone was laid down on top of them.

The irregular topography and basal conglomerate show that this is an erosional contact. Photo: Chris Rowan, 2009

The Siccar Point which is a rocky promontory in the county of Berwickshire on the east coast of Scotland.

6 May 2020

May 06, 2020 Comment

Geologic Contacts

2. Intrusive contacts are those where one rock has intruded another

3. Fault contacts are those where rocks come into contact across fault zones.

Learn in element about fault right here

Following are the a few snap shots displaying each kind of geologic contact

Depositional Contacts

1. Angular Unconformity, Siccar Point, Scotland

This place is known as Siccar Point whichis the most important unconformity described by James Hutton (1726-1797) in support of his world-changing ideas on the origin and age of the Earth.

Here gently sloping strata of 370-million-year-old Famennian Late DevonianOld Red Sandstone and a basal layer of conglomerate overlie near vertical layers of 435-million-year-old lower Silurian Llandovery Epoch greywacke, with an interval of around 65 million years.

2. Cretaceous Sandstone overlying Conglomerate Kootenai Formation, SW Montana

Photo Courtesy: marlimillerphoto.Com

3. Dun Briste Sea Stack, IrelandDun Briste is a truly incredible site to see but must be visited to appreciate its splendour. It was once joined to the mainland. The sea stack stands 45 metres (150 feet) tall.

Dun Briste and the surrounding cliffs were formed around 350 million years ago (during the 'Lower Carboniferous Period'), when sea temperatures were much higher and the coastline at a greater distance away. There are many legends describing how the Sea Stack was formed but it is widely accepted that an arch leading to the rock collapsed during very rough sea conditions in 1393. This is remarkably recent in geological terms.