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Geology of Colombia South America

After reading about Our Lady of Las Lajas, (our Lady of the Rocks) I decided to learn something about the geology of Colombia, particularly around Ipiales. What sort of stones might there be in Colombia, I wondered, and are any of them deep blue shales? Here is the Las Lajas image, composed entirely of stone, except for the crowns, added later and seeming somewhat adrift on the glorious heads of the mother and child. (The other two figures are St. Francis and St. Dominic.)

Our Lady of Las Lajas 02

Lying as it does at the foot of the Isthmus of Panama. Colombia has the distinction being formed at the intersection of at least three tectonic plates: the Nazca Plate under the Pacific Ocean, the Caribbean Plate on the eastern side of the isthmus, and the South American plate to the south. The Nazca plate apparently first pushed against the South American plate in the deeps of time, over 500 million years ago, which is about when the supercontinent of Pangaea formed and before it broke up into the northern semi-supercontinent of Laurasia and its southern counterpart, Gondwana.

Laurasia included North America, and Gondwana included South America. Both of them had to break apart along a north-south seam, releasing Eurasia and Africa westwards, whilst also coming together from north to south, thus creating the double continent of the Americas, with Panama at their juncture.

Panama, therefore, is at the junction of several tectonic plates whose collisions belong to various episodes of tectonic shift over half a billion years. Looking today from above, one may think of it as a delicate strand that connects two continents; in fact it is probably not much more delicate than Italy which also lies at a junction of three tectonic plates a fact which accounts for its world reputation in beautiful marble.

The Andes mountains are the most striking feature of Colombia and also the location of most of her cities. The west coast is jungly and wet; the eastern plains range from something like savannah in the north, to the upper reaches of the Amazon jungle in the south; but even the drier regions have annual flooding that makes farming difficult. So the mountains are the location of Colombia’s cities and it is rugged going from place to place.

The city of Ipiales is on the western side of the Andes Mountains, just above the jungles of the Pacific coast, and just over the border from Ecuador. The little town of Potosi is six miles east. Perhaps both towns were small in 1754.

Blue shales

I still do not know anything about blue shales. Somerset England has a lovely formation from the early Jurassic, called the Lias. The stone is very blue.

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