Fold

Ptygmatic folds

We are all familiar with the shape of squished and baked rocks, that occur at every scale from the centimetre up to the hundreds of kilometres, illustrating the fractal nature of geological processes. When a single layer of harder rocks (called more competent by geologists) is squished amongst softer ones, the latter often get melded into each other, and don’t reveal clearly what happened to them during their metamorphism, information vital for the understanding of the tectonics of a region and such processes as mountain building. Enough data points like these folds in a calcite vein eliminates local variations and allows an assessment of the pressures and forces that shaped a region.

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Awesome drone overlook views of folded sedimentary rocks, Costa Vicentina, Portugal

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Gorgeous structural geology sketches