I loved the article accompanying this photo because it has a great summary of the geologic and tectonic history of Laurasia, Gondwanaland and Pangea in relation to Appalachian mountain building:
The rocks that form this valley-and-ridge province, as it is known, are relatively old (540 to 300 million years old) and were laid down in horizontal layers when North America was attached to Europe in the ancient supercontinent of Laurasia. During this time Gondwanaland—an ancient supercontinent that included present-day Africa, India, South America, Australia, and Antarctica—was approaching Laurasia under the influence of plate tectonics. The northwest coastline of modern Africa was the section of Gondwanaland that “bumped up” against modern North America over a long period (320 to 260 million years ago).
The net result of the tectonic collision was the building of a major mountain chain, much higher than the present Appalachian range. In the process, the flat-lying rock layers were crumpled up into a series of tight folds, at right angles to the advance of Gondwanaland. The collision also formed the singular supercontinent of Pangaea. Over the following 200 million years, Pangaea broke apart; the modern Atlantic Ocean formed; and erosion wore down the once-high mountains. What is left 200 million years later are the coastline of North America and the eroded stumps of the relatively low, but visually striking mountain chain.
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