Thursday, March 23, 2006

Tracks



As a student of geology, I would often have to visit working quarries to record the geology that was being revealed before it was carted away in the back of a truck. Sometimes it was sad to see beautiful geological structures being destroyed. But there wasn't much point getting sentimental about it: better just to take some good pictures and wait to see what would be revealed next.

Arriving in one quarry that was been worked in soft, friable sand, I discovered a face which had been recently cut by a large yellow JCB shovel. I began to examine it, marking the unusual colour of the sand and the particularly high organic content that gave the sands a dark colour. The texture was most unusual and the structures in the face looked nothing like those I had seen in other quarries nearby. I started using my spade to clean up the face and then I discovered an important surface at the base of the sands, marking an abrupt change from the more familiar greenish sands below. I thought I had discovered something really interesting.

Just then the quarry manager turned up in his Land Rover. I explained to him that I thought I had found something new and unusual. He looked at the dark sand and he said: "Oh that? Yes, Geoff put that there two years ago. It's a hole we filled in with sand. You can see it again because we just cut this track through."

Oh did I feel stupid... There was no interest at all in studying this. Geoff had created it two years ago. Geoff and his JCB were the environmental process that had created these rocks.

But why wasn't it interesting? Why was this pile of sand any less interesting than the pile of sand I had been studying in the quarry next door. Well, it was simply because I knew what had created these rocks. It was Geoff. The rocks in the quarry next door were separated from the present not by an interval of two years, but by an interval of one hundred million years. It would require a significant leap of the informed imagination to reconstruct the depositional processes of those rocks.

Generally, the further back in time a rock was created, the more difficult it is to understand how that rock came into being: the evidence is more disparate, fragmentary. It requires more imagination to build a model from this slender body of evidence. The world was different in the past, and the further you go back through time, the more different it was. No one can tell you: "Geoff made those surfaces", you have to look at the surfaces, look at their shape, try to understand what process was responsible: was it the wind, the tide, a storm, a cataclysm?

Often there will be abundant clues, particular signs which indicate one origin over another. Each of earth's environments is associated with a particular set of chemical and physical processes whch will mark the sediment grains. In addition, there may be particular biogenic processes which leave their signature in the sediment: the crawling traces of worms, beetles, snakes, birds and quadrupeds. These, and the traces of plants, can tell you about the environmental conditions. Eventually, a fascinating story will emerge. And the more you look, the more it will fascinate. This is why geologists can become slightly obsessive. They no longer wholly inhabit the present. A part of them remains stuck in another world, probably quite different to our own: a desert place with huge dunes or a vast chalky sea in which giant ammonites swim.

The tracks of man are quite rare. the picture at the top right of my blog is a fossil footprint some 9000 years old. It was revealed by the retreating coastlines of Southport in NW England. Tracks of bare-footed adults and children walking side by side through the soft estuary muds have also been found.

5 comments:

Andrea said...

so you are like a dirt CSI dude.
cool. maybe you can get a spot in the show.

Clare said...

Your descriptions on how you see the world as a geologist are fascinating. I only studied geology for a year at university, but even so I think some of those feelings got into my blood too. That thinking back, and the use of imagination - I often think that geologists share something in this respect with archeologists. Both go so far back that it is impossible to know anything for sure so you just imagine.

I was wondering about the footprint at the top of your blog - although I live fairly close to Southport I have never been there, but now am determined to go before they disappear. They are quite temporary, I understand, the sea constantly washing the mud away to reveal more...and once again the imagination comes into play - imagining all those prehistoric people walking along the shores. They didn't realise it then but they were walking into the future.

Lesley said...

On the subject of geology and poetry (sort of): I'm reading Kenneth White's "Across the Territories" at the moment in which he talks about the earth's magnetic field and it's use as an analogy by the Surrealists. He ends by asking if it might not be possible to "make of existence a field of poetic density?".

Lesley said...

Oops, sorry about that intrusive apostrophe in "it's".

Jonathan said...

Thank you very much for your comments:

Andrea: CSI... Crime Scene Investigation, Right? The celebrated TV series...

No, I'm not exactly a criminal investigator. You mean like a forensic dirt dude, right?

Forensic dirt dude might be okay...

Clare: Glad you found this of interest. There are lots of other geological articles if you look in the index at top right.

If you go to Southport you are unlikely to see the footprints. They are preserved in soft clay and disappear as soon as they are exposed. However, if you went after a storm, you might stand a chance of seeing some fresh ones appearing. All kinds of footprints have been found including bison-type animals. There are also beds of trees that have fallen in high winds. The direction in which they fell indicates the prevailing wind direction at the time.

Lesley - Yes, that's an interesting subject. thanks for mentioning it. I saw you were interested in Kenneth White on your blog. I have never read him but know he has an interest in the earth: "geopoetries" is it he calls it? I guess he's referring to Andre Breton's 'Magnetic Fields'? That I haven't read either but I noticed it for future investigation. Rocks of course take on the earth's magnetic field when they are deposited. Every ferrous rock is like a little magnet which 'remembers' which direction was north when it hardened. Thus there is a whole subarea of geology called 'palaeomagnetism' in which the past wandering of magnetic north and any magnetic reversals (north pole swapping for the south pole) is studied. I don't think anyone really knows why the poles swap over every so often. One of those 'big mysteries'.

It wouldn't be very convenient if you were out orienteering at the time, would it?