near Denver might have index contours of 5,000', 5,100' and so on with a contour interval of 20 feet. This means that there would be five "spaces," and four non-index contour lines, between each index contour. Often, index points are given along with index contours.
True- "Along these boundaries, magma rises from deep within the Earth and erupts to form new crust on the lithosphere. Most divergent plate boundaries are underwater (Iceland is an exception) and form submarine mountain ranges called oceanic spreading ridges."
