登陆注册
14816400000039

第39章

I., page 50.) has described a specimen of Agaricia, "weighing 2 lbs. 9 oz., which surrounds a species of oyster, whose age could not be more than two years, and yet is completely enveloped by this dense coral." I presume that the oyster was living when the specimen was procured; otherwise the fact tells nothing. Mr. Stutchbury also mentions an anchor, which had become entirely encrusted with coral in fifty years; other cases, however, are recorded of anchors which have long remained amidst coral-reefs without having become coated. The anchor of the "Beagle", in 1832, after having been down exactly one month at Rio de Janeiro, was so thickly coated by two species of Tubularia, that large spaces of the iron were entirely concealed; the tufts of this horny zoophyte were between two and three inches in length. It has been attempted to compute, but I believe erroneously, the rate of growth of a reef, from the fact mentioned by Captain Beechey, of the Chama gigas being embedded in coral-rock. But it should be remembered, that some species of this genus invariably live, both whilst young and old, in cavities, which the animal has the power of enlarging with its growth. I saw many of these shells thus embedded in the outer "flat" of Keeling atoll, which is composed of dead rock; and therefore the cavities in this case had no relation whatever with the growth of coral. M. Lesson, also, speaking of this shell (Partie Zoolog.

"Voyage de la 'Coquille'"), has remarked, "que constamment ses valves etaient engages completement dans la masse des Madrepores.")

From the facts given in this section, it may be concluded, first, that considerable thicknesses of rock have certainly been formed within the present geological area by the growth of coral and the accumulation of its detritus; and, secondly, that the increase of individual corals and of reefs, both outwards or horizontally and upwards or vertically, under the peculiar conditions favourable to such increase, is not slow, when referred either to the standard of the average oscillations of level in the earth's crust, or to the more precise but less important one of a cycle of years.

SECTION 4.III.--ON THE DEPTHS AT WHICH REEF-BUILDING POLYPIFERS CAN LIVE.

I have already described in detail, which might have appeared trivial, the nature of the bottom of the sea immediately surrounding Keeling atoll; and I will now describe with almost equal care the soundings off the fringing-reefs of Mauritius. I have preferred this arrangement, for the sake of grouping together facts of a similar nature. I sounded with the wide bell-shaped lead which Captain Fitzroy used at Keeling Island, but my examination of the bottom was confined to a few miles of coast (between Port Louis and Tomb Bay) on the leeward side of the island. The edge of the reef is formed of great shapeless masses of branching Madrepores, which chiefly consist of two species,--apparently M. corymbosa and pocillifera,--mingled with a few other kinds of coral. These masses are separated from each other by the most irregular gullies and cavities, into which the lead sinks many feet. Outside this irregular border of Madrepores, the water deepens gradually to twenty fathoms, which depth generally is found at the distance of from half to three-quarters of a mile from the reef. A little further out the depth is thirty fathoms, and thence the bank slopes rapidly into the depths of the ocean. This inclination is very gentle compared with that outside Keeling and other atolls, but compared with most coasts it is steep. The water was so clear outside the reef, that I could distinguish every object forming the rugged bottom. In this part, and to a depth of eight fathoms, I sounded repeatedly, and at each cast pounded the bottom with the broad lead, nevertheless the arming invariably came up perfectly clean, but deeply indented. From eight to fifteen fathoms a little calcareous sand was occasionally brought up, but more frequently the arming was simply indented. In all this space the two Madrepores above mentioned, and two species of Astraea, with rather large stars, seemed the commonest kinds (Since the preceding pages were printed off, I have received from Mr. Lyell a very interesting pamphlet, entitled "Remarks upon Coral Formations," etc., by J. Couthouy, Boston, United States, 1842.

There is a statement (page 6), on the authority of the Rev. J. Williams, corroborating the remarks made by Ehrenberg and Lyell (page 71 of this volume), on the antiquity of certain individual corals in the Red Sea and at Bermuda; namely, that at Upolu, one of the Navigator Islands, "particular clumps of coral are known to the fishermen by name, derived from either some particular configuration or tradition attached to them, and handed down from time immemorial." With respect to the thickness of masses of coral-rock, it clearly appears, from the descriptions given by Mr. Couthouy (pages 34, 58) that Mangaia and Aurora Islands are upraised atolls, composed of coral rock: the level summit of the former is about three hundred feet, and that of Aurora Island is two hundred feet above the sea-level.); and it must be noticed that twice at the depth of fifteen fathoms, the arming was marked with a clean impression of an Astraea.

Besides these lithophytes, some fragments of the Millepora alcicornis, which occurs in the same relative position at Keeling Island, were brought up; and in the deeper parts there were large beds of a Seriatopora, different from S. subulata, but closely allied to it. On the beach within the reef, the rolled fragments consisted chiefly of the corals just mentioned, and of a massive Porites, like that at Keeling atoll, of a Meandrina, Pocillopora verrucosa, and of numerous fragments of Nullipora.

同类推荐
热门推荐
  • 我的男友——鹿晗

    我的男友——鹿晗

    鹿晗,遇见你的时间刚刚好。或许从那个时候起,彼此就是唯一。那就一辈子好了,这是我听过最动人的话。
  • tfboys没你一样很好

    tfboys没你一样很好

    还记得那年那个美好温柔的他,现在……都物是人非,谁也不记得谁了。
  • 苍浪传奇之都市风云

    苍浪传奇之都市风云

    “我只是一个游戏玩家,我的职业就是玩游戏,但是无论是游戏中还是现实里,谁也别想欺负我!”苍浪如此说道。且看被一场奇遇彻底改变的苍浪如何在游戏中游戏外谱写一首彪悍的沧浪之歌!
  • 绑架回宫:皇上是只狐狸

    绑架回宫:皇上是只狐狸

    咦,在他面前这只眨着萌萌哒的眼睛对她卖萌是谁?某皇帝狐狸表示很无奈,没办法修炼中初次见面跟我回家吧!某皇帝欣然答应......“啊啊啊啊啊,光天化日强抢民女啦!”“嘘,爱妃你怎么能这样说你夫君呢。”某皇后提起裙摆就跑。某男淡定的吹了吹手。“爱妃。”“hi~相公我们又见面了~”
  • 相思谋:妃常难娶

    相思谋:妃常难娶

    某日某王府张灯结彩,婚礼进行时,突然不知从哪冒出来一个小孩,对着新郎道:“爹爹,今天您的大婚之喜,娘亲让我来还一样东西。”说完提着手中的玉佩在新郎面前晃悠。此话一出,一府宾客哗然,然当大家看清这小孩与新郎如一个模子刻出来的面容时,顿时石化。此时某屋顶,一个绝色女子不耐烦的声音响起:“儿子,事情办完了我们走,别在那磨矶,耽误时间。”新郎一看屋顶上的女子,当下怒火攻心,扔下新娘就往女子所在的方向扑去,吼道:“女人,你给本王站住。”一场爱与被爱的追逐正式开始、、、、、、、
  • 惑世妖后

    惑世妖后

    吃面噎死的黑道女王,一朝穿越,居然成为惑世的妖女。欺我,辱我,定要你们百倍奉还!明明可以无情无欲,却被半路杀出来的妖孽打乱!且看我们的乱世妖女,怎么斗小三,赦天下,欺妖皇。
  • 幻灭狂徒

    幻灭狂徒

    背景:十六岁地球少年齐痕意外被吸入虚空裂缝,来到一个叫做“幻界”全新的世界。在这个世界,没有科技力量,没有修真修仙,没有斗气魔法,唯一存在于这个世界的职业就是“幻师”!幻器,可通过右手召唤,终身唯一性,可在四岁至十六岁觉醒,称为“初觉”,第二次觉醒称为“次觉”,第三次称为“三觉”,第四次称为“终觉”。每一次觉醒可开启幻器全新形态......影器,可通过影器手套在左手召唤,可更换,有品级之分,可附加技能,可镶嵌宝石,可铭刻阵法......全新的世界,全新的战场,看齐痕如何右手持幻器,左手持影器,幻影相通,破灭虚空!
  • 地底迷域

    地底迷域

    脉可承混沌之气,化夺天造地之功,各族自成一脉,繁衍千年,数千年后,十六岁的少年竹轩长大,少年空有一身武艺,无奈血脉平庸,受尽欺凌,直至一日,少年遵循着家老的遗嘱,寻到了一处遗址,遗址内,封印着一位少女,从中得到一枚古戒,这枚古戒,改变了少年的世界。世人辱我,负我,欺凌于我,又如何?至此少年坠入混沌,重铸血脉,执掌一域迷城,大手一挥,妖兽大军无人可敌,诛尽一切来犯之人。
  • 凰倾天下:嫡女杀手

    凰倾天下:嫡女杀手

    她,龙啸国大将军之女,却过着连一个下人都不如的日子。银眸一睁,且看废物嫡女如何称霸天下!他,龙啸国玄觞王,要风得风,要雨得雨,却对她情有独钟,死乞白赖贴上去:小羽儿,你要对我负责!
  • 无敌小农民

    无敌小农民

    一个乡村痞子,奇遇不断,左手治病,右手种田。从此,睡觉睡到自然醒,数钱数到手抽筋。