Answer:
The structure of the Pyrenees is characterized by patterns of relief and of underlying structure running in a north–south sequence (like the base rock); these alternate with depressions, some of which are the result of internal deformations, others of erosion of less resistant overlying deposits.
Forming a natural geographic border between France and Spain, the Pyrenees Mountains were built over millions of years as continents collided. Previous studies indicate that before it became the Pyrenees Mountains, the continental crust in the region was stretched and thinned by rifting. Although the eastern section of this rift system was folded and compressed to make the Pyrenees, the weather section is preserved in the Bay of Biscay.
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