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2021考研英语备考:看阅读记单词(六)
Scatteredaround the globe are more than 100 small regions of isolated volcanic activity known to geologistsas hot spots. Unlike most of the world’s volcanoes, they are not always found at the boundaries of the great driftingplates that make up the earth’s surface; on the contrary, many of them lie deep in the interiorof a plate. Most of the hot spots move only slowly, and in some cases the movement of the plates past them has left trails of dead volcanoes. The hot spots and their volcanic trails are milestonesthat mark the passage of the plates.
That the plates are moving is not beyond dispute. Africa and South America, for example, are moving away from each other as new material is injected into the sea floor between them. The complementary coastlines and certain geological features that seem to span the ocean are remindersof where the two continents were once joined. The relative motion of the plates carrying these continentshas been constructed in detail, but the motion of one plate with respect to another cannot readilybe translated into motion with respect to the earth’s interior. It is not possible to determinewhether both continents are moving in opposite directions or whether one continent is stationary and the other is drifting away from it. Hot spots, anchored in the deeper layers of ...