| Article Index |
|---|
| Hutton's Unconformity |
| Problems |
| A Fine Example Of Science |
| Further Reading |
| All Pages |
A brief outline of geological theories before Hutton, and what led him to his Uniformitarian ideas.
The youth hostel at Lochranza, on the island of Arran, has a geological map hanging on the wall. It is a fairly small scale map, and hidden away in one corner of the dining room, but the huge red blob showing the granite in the northern half of the island draws your eye from across the room. On closer inspection, you can just about make out the words 'Hutton's Unconformity' hovering on the map near the coast, about a mile away from the hostel itself. Such a landmark in the history of earth science just had to be visited – although it would have been useful if I had also read another poster on the wall that told me exactly where it was.
An unconformity in geology is a boundary between two sets of rock where some of the 'history' is missing – the layers do not match up. In this case, the schists (hard metamorphic rocks) that make up the land near Lochranza are tilted, so much that they are not far off vertical. On top of these schists lies a layer of sandstone that is almost horizontal. I knew roughly what I was looking for, but it took me a while to be sure that what I was looking at really was the unconformity that helped James Hutton to formulate his theories about the Earth in the late 18th century. The rocks are there for all to see, but need to be looked at closely and with some knowledge to appreciate what they are telling us.
At that time science as we know it was only just getting started, and earth sciences were even further behind. Most people in the Western world took it for granted that the Christian Bible was the literal truth and that therefore the world was about 6000 years old, as calculated by Ussher from the genealogies in the Old Testament. Much 'scientific' effort at the time, such as it was in earth science, tried to explain how the world we see had formed from God's perfect creation – the Flood having much to do with it. Opinion was divided between Neptunists (all the layers in rocks were laid down when sediments settled out during the Flood, or from some primeval ocean) and Vulcanists (volcanic eruptions had disturbed the surface of the Earth and formed layers of rocks).
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