Thursday, March 23, 2006
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.