登陆注册
4703400000070

第70章

The existence in many parts of the world of high table-land, proves that large surfaces have been upraised in mass to considerable heights above the level of the ocean; although the highest points in almost every country consist of upturned strata, or erupted matter: and from the immense spaces scattered with atolls, which indicate that land originally existed there, although not one pinnacle now remains above the level of the sea, we may conclude that wide areas have subsided to an amount, sufficient to bury not only any formerly existing table-land, but even the heights formed by fractured strata, and erupted matter. The effects produced on the land by the later elevatory movements, namely, successively rising cliffs, lines of erosion, and beds of literal shells and pebbles, all requiring time for their production, prove that these movements have been very slow; we can, however, infer this with safety, only with respect to the few last hundred feet of rise. But with reference to the whole vast amount of subsidence, necessary to have produced the many atolls widely scattered over immense spaces, it has already been shown (and it is, perhaps, the most interesting conclusion in this volume), that the movements must either have been uniform and exceedingly slow, or have been effected by small steps, separated from each other by long intervals of time, during which the reef-constructing polypifers were able to bring up their solid frameworks to the surface. We have little means of judging whether many considerable oscillations of level have generally occurred during the elevation of large tracts; but we know, from clear geological evidence, that this has frequently taken place; and we have seen on our map, that some of the same islands have both subsided and been upraised. I conclude, however, that most of the large blue spaces, have subsided without many and great elevatory oscillations, because only a few upraised atolls have been observed: the supposition that such elevations have taken place, but that the upraised parts have been worn down by the surf, and thus have escaped observation, is overruled by the very considerable depth of the lagoons of all the larger atolls; for this could not have been the case, if they had suffered repeated elevations and abrasion. From the comparative observations made in these latter pages, we may finally conclude, that the subterranean changes which have caused some large areas to rise, and others to subside, have acted in a very similar manner.

RECAPITULATION.

In the three first chapters, the principal kinds of coral-reefs were described in detail, and they were found to differ little, as far as relates to the actual surface of the reef. An atoll differs from an encircling barrier-reef only in the absence of land within its central expanse; and a barrier-reef differs from a fringing-reef, in being placed at a much greater distance from the land with reference to the probable inclination of its submarine foundation, and in the presence of a deep-water lagoon-like space or moat within the reef. In the fourth chapter the growing powers of the reef-constructing polypifers were discussed; and it was shown, that they cannot flourish beneath a very limited depth. In accordance with this limit, there is no difficulty respecting the foundations on which fringing-reefs are based; whereas, with barrier-reefs and atolls, there is a great apparent difficulty on this head; in barrier-reefs from the improbability of the rock of the coast or of banks of sediment extending, in every instance, so far seaward within the required depth;--and in atolls, from the immensity of the spaces over which they are interspersed, and the apparent necessity for believing that they are all supported on mountain-summits, which although rising very near to the surface-level of the sea, in no one instance emerge above it. To escape this latter most improbable admission, which implies the existence of submarine chains of mountains of almost the same height, extending over areas of many thousand square miles, there is but one alternative; namely, the prolonged subsidence of the foundations, on which the atolls were primarily based, together with the upward growth of the reef-constructing corals. On this view every difficulty vanishes; fringing reefs are thus converted into barrier-reefs; and barrier-reefs, when encircling islands, are thus converted into atolls, the instant the last pinnacle of land sinks beneath the surface of the ocean.

Thus the ordinary forms and certain peculiarities in the structure of atolls and barrier-reefs can be explained;--namely, the wall-like structure on their inner sides, the basin or ring-like shape both of the marginal and central reefs in the Maldiva atolls--the union of some atolls as if by a ribbon--the apparent disseverment of others--and the occurrence, in atolls as well as in barrier-reefs, of portions of reef, and of the whole of some reefs, in a dead and submerged state, but retaining the outline of living reefs. Thus can be explained the existence of breaches through barrier-reefs in front of valleys, though separated from them by a wide space of deep water; thus, also, the ordinary outline of groups of atolls and the relative forms of the separate atolls one to another; thus can be explained the proximity of the two kinds of reefs formed during subsidence, and their separation from the spaces where fringing-reefs abound. On searching for other evidence of the movements supposed by our theory, we find marks of change in atolls and in barrier-reefs, and of subterranean disturbances under them; but from the nature of things, it is scarcely possible to detect any direct proofs of subsidence, although some appearances are strongly in favour of it. On the fringed coasts, however, the presence of upraised marine bodies of a recent epoch, plainly show, that these coasts, instead of having remained stationary, which is all that can be directly inferred from our theory, have generally been elevated.

Finally, when the two great types of structure, namely barrier-reefs and atolls on the one hand, and fringing-reefs on the other, were laid down in colours on our map, a magnificent and harmonious picture of the movements, which the crust of the earth has within a late period undergone, is presented to us. We there see vast areas rising, with volcanic matter every now and then bursting forth through the vents or fissures with which they are traversed. We see other wide spaces slowly sinking without any volcanic outburst, and we may feel sure, that this sinking must have been immense in amount as well as in area, thus to have buried over the broad face of the ocean every one of those mountains, above which atolls now stand like monuments, marking the place of their former existence.

Reflecting how powerful an agent with respect to denudation, and consequently to the nature and thickness of the deposits in accumulation, the sea must ever be, when acting for prolonged periods on the land, during either its slow emergence or subsidence; reflecting, also, on the final effects of these movements in the interchange of land and ocean-water on the climate of the earth, and on the distribution of organic beings, I may be permitted to hope, that the conclusions derived from the study of coral-formations, originally attempted merely to explain their peculiar forms, may be thought worthy of the attention of geologists.

同类推荐
  • 大唐贞元续开元释教录

    大唐贞元续开元释教录

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
  • 南山经

    南山经

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
  • 道德真经取善集

    道德真经取善集

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
  • 效力篇

    效力篇

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
  • 刘子

    刘子

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
热门推荐
  • 太上灵宝净明法序

    太上灵宝净明法序

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
  • 宝贝宠你会上瘾

    宝贝宠你会上瘾

    “现在给你两个选择,一,我吻你,二,你吻我。如果你一个都不选,那么我就直接吃掉你。”他,是忘斯京贵族学院里最高贵的泉少,不把任何女人对他的感情放在眼里,却唯独只对她一片痴心。已经被他灌醉,并且带到床上的她,神志不清的说:随……便……你,还有,这衣服我穿的不舒服!”
  • 显扬圣教论

    显扬圣教论

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
  • 埃里汪奇游记

    埃里汪奇游记

    这故事描述一个英格兰人的一次奇妙经历。为了发财而远寻一片合适蓄牧的荒地,历尽艰辛,主人翁最终到达一个名为埃里汪的国家。这个国家的法规和习俗与其他国家有许多分别,主人翁记下了埃里汪的风土人情和一些主要的观点,如对机器、未生人和死亡的看法。主人翁的遭遇使读者进入奇异的国度,惊讶万分。其实,作者在书中多用讽刺和颠倒逻辑的手法来反映维多利亚时代的现象。这趟旅程蕴含作者对当时社会的看法和感受,发人深省,耐人寻味。这也是最早提出机器作为一种生物会进化出自我意识的作品。
  • 神道凡人

    神道凡人

    天道有缺,神道不凡,少年风宁灵脉被封,少年失忆,机缘巧合加入灵元谷,一路披荆斩棘,在这修真大道,他拥有的始终不过是一颗凡心。
  • 一里一里的阳光

    一里一里的阳光

    《一里一里的阳光》是作者出版的第二本小小说集子。这本集子由亲情、言情、都市、荒诞、百姓、校园、市井、官场八个部分组成。该书收录了作者近两年创作、发表的70多篇作品。该书从多个角度反映了底层人们的生活状态。这里面有哭也有笑,在哭与笑之中,读者可以理解作者的用心良苦。
  • 汉末复新

    汉末复新

    西汉末年,汉室外戚王莽横空出世,篡夺了汉室江山,使其改朝换代,建立新朝,想成就一番不世伟业,之后他就推行改革,史称‘王莽改制’,可惜功败垂成,新朝犹如烟花般,炫丽的转瞬即逝。而在两百年后,东汉末年,王莽第九世孙王杰传承王莽遗志,归宗鬼谷门下,随后出山和大哥欧阳昊,二哥肖然,三兄弟齐心协力,让烟花般的新朝变成了永恒的太阳,使其耀眼的光芒普照大地。
  • 重生之新生

    重生之新生

    她,一个父母厌弃的小孩,和奶奶相依为命的长大。然而,十八岁,奶奶也永远的去了,只留一个玉镯给她。她在想活着是为了什么?一个人,一个人,一直一直……可是,她还得活着,奶奶说,你要活着。她很听话。浑浑噩噩的过了几年,孤单寂寞的她,本以为这一生就将如此老去,但是在一个雨夜的电闪雷鸣中,她的人生出现了转机。她,重生了。重新拥有了亲人,重新找到了生活的意义!玉镯的空间让她有了资本拥有自己想要的生活,也有让她有了别人永远想不到的奇遇。不张扬,不随意。用心爱着自己的家人和朋友。可是老有人企图破坏他们的生活,危害她认可的人。于是,她爆发了!阴谋诡计在强大的力量下都是纸老虎,谁要妨碍她,她就给谁好看!
  • 旁爱

    旁爱

    时间弹指,间隙流年。有的人坚持本心,有的人放错了原来的那个自己。我们都曾经历悲失,与欢颜同在。旁爱,述说着别人的爱,迷失中回归自我,韶华之光从不泯灭。
  • 快穿系统男神笑一个

    快穿系统男神笑一个

    别人家的爱豆:沉鱼落雁,闭月羞花自己家的爱豆:自恋毒舌不说,竟然还藏了一个男人!粉丝们却不知,一代影后曾经无辜遭死被无良系统拉去做任务,好嘛,为了能重回世界,她忍。叛逆少女、温柔女神、悲情千金、末世妖精各种类型都能驾驭,却不曾想,一不小心在三千世界里陷入美色,无法自拔。纯洁干净vs傲娇腹黑,小奶狗vs小狼狗,该选哪一种美色?黎雪表示两个都想要。“宿主,难道你不要我了吗?”“不要让我亲自动手,嗯?”黎雪躲在角落里瑟瑟发抖,麻麻,我要回家!第一次写快穿文,请多关照。文笔稚嫩,欢迎吐槽。男女主身心干净,1v1~