51．Unlike most of the world's volcanoes, they are not always found at the boundaries of the great drifting plates that make up the earth's surface; on the contrary, many of them lie deep in the interior of a plate.

　　[参考译文]跟世界上的大多数火山不同的是，它们(热点)并不总是在由构成地球表面巨大漂流板块之间的边界上出现；相反，它们中有许多位于一个板块较纵深的内部。

　　52．The relative motion of the plates carrying these continents has been constructed in detail, but the motion of the plates with respect to another cannot readily be translated into motion with respect to the earth's interior.

　　[参考译文]携带这些大陆板块的相对运动已经能够被详细地表述出来，但是这些板块相对于另一些板块的运动还不能轻易地解释为它们相对于地球内部的运动。

　　53．As the dome grows, it develops seed fissures (cracks); in at least a few cases the continent may break entirely along some of these fissures, so that the hot spot initiates the formation of a new ocean.

　　[考译文]随着这个圆顶的增长，它开始出现初始的裂缝(裂纹)；在至少几个个例中，这块大陆可能会沿着其中的一些裂缝完全裂开，因此这个热点就引发了一个新的海洋的形成。