Book of the Month: October – James Hutton

James Hutton : The father of modern geology
Donald B. McIntyre and Alan McKirdy

I seem to be having a geology fit at the moment – I came across this book in the library catalogue while looking for a different bit of geological history, and then found when I went to get it that it wasn’t really a proper book, just the flat kind full of pictures – but that was a good thing, both because I was behind with my reading, and because the pictures are very informative.

The book was published by the National Museum and Dynamic Earth, and is more about Hutton’s ideas than his life, but I’m certainly not complaining about that.

Hutton started off in a world still believed to be about 6000 years old – which was probably not as silly a belief as it sounds now, because if you don’t know of anything happening earlier, you don’t need to leave time for it. However, Hutton’s great achievement was to show that things which seemed inexplicable became perfectly reasonable if you just allow enough time for them to occur.

Hutton began by developing an interest in chemistry while studying at the University of Edinburgh in his teens, discovering a new process for producing sal ammoniac, used in various industries, and went on to study medicine in Paris and Leiden. Returning to Scotland, he settled on a family farm, giving up medicine and taking to agriculture as a science. It was from an agricultural point of view that he first seems to have taken an interest in the ground, touring England, and later parts of the continent, to study farming methods, and becoming interested in geological features along the way.

Later tours of Scotland were more deliberately geological, and brought him a strong practical knowledge of the rocks to be found in various places which was very important to him later on when developing and proving his theories.

Hutton’s real strength seems to have been his ability to use rocks as experiments which had already taken place – in the same way a chemist might predict that a particular reaction would occur, and test it to see, Hutton would come to believe that a certain event had occurred, and that the result would show in a certain kind of place or kind of rock – at which point his knowledge of where to find the different types would come into play.

It had long been recognised that rocks wore away, and even that soil was formed from the remnants of rocks, but without a method of renewal this was only the decay of the earth towards its eventual end. Hutton came to believe that most of the rocks he had seen were formed from layers of sand and gravel produced by the wearing away of older rocks, and made solid by heat from within the earth, which also distorted and transformed them. (This great heat within the earth, somehow burning without oxygen, was needed to produce effects seen on the surface, but something which he was very aware could not be directly observed – its effects could only be predicted and checked for confirmation.)

One of the pieces of confirmation for this theory was the presence of igneous intrusions, rocks which had cut through earlier regular strata while in a molten state and solidified there, and could be easily traced because they often wore away much more slowly than the surrounding rocks. A related interest was in granite, often believed at the time to be the oldest rock in existence. Hutton believed it to be relatively young, and formed from a molten state, and knew that this could be tested – if veins of granite could be found intruding into other rocks, then the other rocks had been there first. To demonstrate this, he would have to use his wide knowledge of rock types to find a place where granite and another rock came in close contact, which he found in Glen Tilt.

After this, he came across a junction of greywacke and sandstone in the Borders, originally at Jedburgh, where the underlying stone had been deformed and worn away before the upper layers were deposited – something which would simply take a great deal of time. It was the search for a clearer example of this which took him to Siccar Point.

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