Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots. 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. 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 milestones that 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 reminders of where the two continents were once joined. The relative motion of the plates carrying these continents has been constructed in detail, but the motion of one plate with respect to another cannot readily be translated into motion with respect to the earth’s interior. It is not possible to determine whether 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 the earth, provide the measuring instruments needed to resolve the question. From an analysis of the hot spot population it appears that the African plate is stationary and that it has not moved during the past 30 million years.       

　　The significance of hot spots is not confined to their role as a frame of reference. It now appears that they also have an important influence on the geophysical processes that propel the plates across the globe. When a continental plate come to rest over a hot spot, the material rising from deeper layer creates a broad dome. 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. Thus just as earlier theories have explained the mobility of the continents, so hot spots may explain their mutability (inconstancy)。

　　译文

　　地球上散落分布着100多个互不相连的小火山活跃区，地质学家称之为热点。与地球上大多数火山不同的是，它们并不总是在构成地球表面的巨大漂流板块之间的连接处上出现；相反，许多热点处于板块较深的内部。大多数热点移动极为缓慢，有些时候，板块滑过这些热点便留下了死火山的痕迹。热点及其火山痕迹是板块漂移的标志。　　现在对于板块漂移这一理论是毋庸置疑的。例如，由于有新的物质注入二者之间的海底，非洲和南美洲距离越来越远。即使跨越海洋，但是由于相互吻合的海岸线和某些可乐了海洋类似的地质特征都能使人会想到整个两个大陆曾经是连在一起的。对于这些大陆的板块的相对运动已经能够被详细地解释出来，但是以地球内部为参照物，不能很好地说明一个板块相对于另一个板块的相对运动之间的关系。人们不能确定是两个大陆都朝相反的方向运动漂移而去，还是一个大陆静止不动另一个大陆从他身边漂移而走。处于地球更深层的热点提供了解决该问题的测量仪器。通过对热点区域的研究情况发现，非洲板块似乎是静止不动的，至少在过去的3000万年里没有移动过。

　　热点的重要性不仅只是局限于其作为参照系统所表现的作用。现在看来，热点还对推动板块在地球表面漂移这一地球物理过程有重大影响。当大陆板块漂移到热点上方时，来自地球深层的物质便形成了巨大的拱形隆起物。随着该拱形的增长，板块出现深深的裂缝。至少有些情况下，大陆可能会沿着其中的某些裂缝完全裂开，该热点就引发了一个新的海洋的形成。因此，正如早期的理论解释了大陆的漂移性一样，热点理论或许能够解释大陆板块的易变性。

　　词汇

　　Coastlinen  n. 海岸线

　　例句：Unrestricted hotel development have ruined the coastline. 无限制地发展饭店已经使沿海地区遭到破坏。

　　Continent  n. 大陆， 洲a. 自制的

　　派生：continence, continency n. 克己；自制 continental a. 大陆的 continently ad. 自制地

　　例句：Africa is a very large continent. 非洲是一块非常大的大陆。

　　词组：the continent of Asia亚细亚大陆

　　反义词：incontinent; island; isle

　　Drifting  adj. 漂流的， 飘动的

　　例句：He is drifting through life. 他随波逐流地过日子。

　　Determine  vt. 决定， 决心vi. 决定， 决心

　　派生：determined a. 坚决地 determiner n. 限定词

　　例句：A rather elaborate analysis was required to determine the cross-over values. 要求相当精确地分析才能确定其交换值。

　　词组：be determined to do sth. 决心做某事determine on/ determine upon  决定determine  sb. against sth./ determine sb. to do sth. 使某人决定不做某事

　　Entirely  ad. 完全， 全然， 一概

　　例句：I meant to mail the letter, but it entirely slipped my memory. 我本来准备发这封信的，却完全给忘掉了。

　　同义词：altogether completely exclusively fully solely thoroughly totally wholly

　　Frame  n. 框， 结构， 体格vt. 构成， 设计， 制定， 使适合， 陷害

　　例句：He had a deep, resonant voice, fitted to his massive frame. 他的嗓音低沉，带着回音，同他魁梧的体格非常相配。

　　词组：picture frame 画框， 相框 (=sheriffs picture frame)绞架be not framed for 不适于； 经不起； 受不住out of frame 纷乱， 无秩序frame of mind 心情， 心境frame to oneself 想象frame up (美俚)诬陷frame well 有才能， 有希望

　　同义词：arrange body border bound build construct design devise edge figure form make plan put together skeleton support trim

　　Geologist  n. 地质学家；地质学者

　　例句：One was blue, and a geologist; one was a horsewoman and smoked cigars. 她们中间一个是女才子，地质学家；一个是女骑手，还会吸雪茄。

　　Geophysical   a. 地球物理学的

　　例句：The method has proved more and more to be of very great geophysical significance. 这个方法在地球物理学上的重要性越来越明显。

　　Interior   n. 内部， 内政a. 内部的， 心灵的， 内地的， 内政的

　　例句：He discussed the propagation of waves through the earth's interior. 他探讨了地震波在地球内部的传播。

　　词组：an interior city内地城市

　　同义词：core heart inner inside middle nucleus

　　反义词：exterior; foreign

　　Milestone   n. 里程碑， 里程石， 里程标

　　例句：This Games will be a milestone in Olympic history, and in the history of China. 北京的奥运会将成为奥林匹克历史和中国历史中的一个里程碑。

　　Mobility   n. 可动性， 流动性， 机动性

　　例句：There has been a tremendous increase in mobility. 人才流动已经有了大幅度增加。

　　Mutability   n. 易变性， 性情不定

　　词组：mutability of human affairs人世沧桑

　　Reminder   n. 提醒的人， 暗示

　　例句：They need reminders to slow down to the pace of family life and show their care for loved ones. 人们需要经常被提醒一下，以便停下来关照一下家庭生活，并向心上人表达关爱。

　　词组：a reminder slip催询单a reminder tray意见箱a gentle reminder暗示

　　Readily   ad. 迅速地， 轻易地， 乐意地

　　例句：He readily agreed to help us. 他欣然同意帮助我们。

　　Scattered  a. 分散的， 散乱的

　　例句：Factories should be scattered instead of being concentrated in a single area. 工厂应分散布局而不应集中在一个地区。

　　词组：scattered set无核集scattered sheaf散射层

　　Significance   n. 重要性， 意义， 意味

　　例句：Most leaders'vanity causes them to exaggerate their own significance. 绝大多数领导人出于虚荣心往往喜欢夸大他们自己的重要地位。

　　词组：of no (little) significance 无关紧要的

　　同义词：connotation consequence drift effect gist implication importance meaning substance