蜜芽传媒

Edinburgh castle is built on a granite plug. A volcano erupted in Edinburgh millions of years ago. The volcano became blocked when molten magma cooled and solidified within the vent. Millions of years later the sea level rose and sedimentary rocks were laid down. As the sea level fell again, the softer sedimentary rocks were eroded away leaving the more resistant granite plug as a higher area of land. This became an ideal defence site and a castle was built.