登陆注册
19488200000064

第64章 CHAPTER VII(4)

{43} These pits or pipes are still in process of formation. During the last forty years I have seen or heard of five cases, in which a circular space, several feet in diameter, suddenly fell in, leaving on the field an open hole with perpendicular sides, some feet in depth. This occurred in one of my own fields, whilst it was being rolled, and the hinder quarters of the shaft horse fell in; two or three cart-loads of rubbish were required to fill up the hole. The subsidence occurred where there was a broad depression, as if the surface had fallen in at several former periods. I heard of a hole which must have been suddenly formed at the bottom of a small shallow pool, where sheep had been washed during many years, and into which a man thus occupied fell to his great terror. The rain-water over this whole district sinks perpendicularly into the ground, but the chalk is more porous in certain places than in others. Thus the drainage from the overlying clay is directed to certain points, where a greater amount of calcareous matter is dissolved than elsewhere. Even narrow open channels are sometimes formed in the solid chalk. As the chalk is slowly dissolved over the whole country, but more in some parts than in others, the undissolved residue-- that is the overlying mass of red clay with flints,--likewise sinks slowly down, and tends to fill up the pipes or cavities. But the upper part of the red clay holds together, aided probably by the roots of plants, for a longer time than the lower parts, and thus forms a roof, which sooner or later falls in, as in the above mentioned five cases. The downward movement of the clay may be compared with that of a glacier, but is incomparably slower; and this movement accounts for a singular fact, namely, that the much elongated flints which are embedded in the chalk in a nearly horizontal position, are commonly found standing nearly or quite upright in the redclay. This fact is so common that the workmen assured me that this was their natural position. I roughly measured one which stood vertically, and it was of the same length and of the same relative thickness as one of my arms. These elongated flints must get placed in their upright position, on the same principle that a trunk of a tree left on a glacier assumes a position parallel to the line of motion. The flints in the clay which form almost half its bulk, are very often broken, though not rolled or abraded; and this may he accounted for by their mutual pressure, whilst the whole mass is subsiding. I may add that the chalk here appears to have been originally covered in parts by a thin bed of fine sand with some perfectly rounded flint pebbles, probably of Tertiary age; for such sand often partly fills up the deeper pits or cavities in the chalk.

{44} S. W. Johnson, 'How Crops Feed,' 1870, p. 139.

{45} 'Nature,' November 1877, p. 28.

{46} 'Proc. Phil. Soc.' of Manchester, 1877, p. 247.

{47} 'Trans. of the New Zealand Institute,' vol. xii., 1880, p. 152.

{48} Mr. Lindsay Carnagie, in a letter (June 1838) to Sir C. Lyell, remarks that Scotch farmers are afraid of putting lime on ploughed land until just before it is laid down for pasture, from a belief that it has some tendency to sink. He adds: "Some years since, in autumn, I laid lime on an oat-stubble and ploughed it down; thus bringing it into immediate contact with the dead vegetable matter, and securing its thorough mixture through the means of all the subsequent operations of fallow. In consequence of the above prejudice, I was considered to have committed a great fault; but the result was eminently successful, and the practice was partially followed. By means of Mr. Darwin's observations, I think the prejudice will be removed."{49} This conclusion, which, as we shall immediately see, is fully justified, is of some little importance, as the so-called bench- stones, which surveyors fix in the ground as a record of their levels, may in time become false standards. My son Horace intends at some future period to ascertain how far this has occurred.

{50} Mr. R. Mallet remarks ('Quarterly Journal of Geolog. Soc.' vol. xxxiii., 1877, p. 745) that "the extent to which the ground beneath thefoundations of ponderous architectural structures, such as cathedral towers, has been known to become compressed, is as remarkable as it is instructive and curious. The amount of depression in some cases may be measured by feet." He instances the Tower of Pisa, but adds that it was founded on "dense clay."{51} 'Zeitschrift fur wissensch. Zoolog.' Bd. xxviii., 1877, p. 360.

{52} See Mr. Dancer's paper in 'Proc. Phil. Soc. of Manchester,' 1877, p. 248.

{53} 'Lecons de Geologie pratique,' 1845, p. 142.

{54} A short account of this discovery was published in 'The Times' of January 2, 1878; and a fuller account in 'The Builder,' January 5, 1878.

{55} Several accounts of these ruins have been published; the best is by Mr. James Farrer in 'Proc. Soc. of Antiquaries of Scotland,' vol. vi., Part II., 1867, p. 278. Also J. W. Grover, 'Journal of the British Arch. Assoc.' June 1866. Professor Buckman has likewise published a pamphlet, 'Notes on the Roman Villa at Chedworth,' 2nd edit. 1873 Cirencester.

{56} These details are taken from the 'Penny Cyclopaedia,' article Hampshire.

{57} "On the denudation of South Wales," &c., 'Memoirs of the Geological Survey of Great Britain,' vol. 1., p. 297, 1846.

{58} 'Geological Magazine,' October and November, 1867, vol. iv. pp.

447 and 483. Copious references on the subject are given in this remarkable memoir.

同类推荐
  • 大宋僧史略

    大宋僧史略

    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。
  • 急救良方

    急救良方

    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。
  • 谒先主庙

    谒先主庙

    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。
  • 唐钟馗全传

    唐钟馗全传

    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。
  • The House of the Wolfings

    The House of the Wolfings

    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
  • 火爆未婚妻

    火爆未婚妻

    不该存在的恋爱,最终还是出现了,他爱上了仇人的女儿...“这样的爱恋,还不如当初不见。”“即便如此还是爱上了你”因为喜欢你,不得不去陷害你的父亲;因为喜欢你,我才不能杀你;因为喜欢你,所以好好活着;因为喜欢你,我才去盲目地服从;我能做的最后一件有意义的事就是,离开你,不为什么只是因为喜欢你......YOUTHINVALUBLENERS如樱花飞舞,迷人,短暂。青春散场,我们就在下一场相逢......----------《樱花流年》—————————————————————————————————————————————————————————本书感谢墨星免费小说封面支持,百度搜索“墨星封面”第一个就是!
  • 鸡谱

    鸡谱

    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。
  • 十年之约,我们一起守候

    十年之约,我们一起守候

    本小说纯是小说题材,喜欢三小只的可以适当的看一下,小说的虚构的,希望大家不要胡乱的喷,谢谢合作!本小说前几章的序章,不是正文,往后看看就是正文。谢谢!!
  • 最强王者

    最强王者

    罗万忠吊炸天,一个比龙傲天更牛逼的少年杀手,被师傅从非洲唤到华夏国保护一对香艳的美女,迎战各路高手,在战斗中提升实力,走向巅峰,赢得人生的若干红颜美妻。少年杀手王,华夏母女花,各路人挑事,谈着恋爱成赢家。
  • 君生我未生

    君生我未生

    如果,没有那些喧哗嘈杂,必能听见我是爱你的……风太大,耳太背,你到底是什么都没听见。爱情之间参杂的事情太多,沉浮中以为情深缘浅,就算言不由衷,那么,许我温柔的爱着你,此生不换。
  • 药性切用

    药性切用

    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。
  • 刀绝

    刀绝

    一个小人物的武道生涯,从一个王府少爷到跺跺脚大陆颤动的强者。
  • 肥猫笔记

    肥猫笔记

    安逸,人如其名,过着自己所向往的安逸的生活。直到有一天,由于一个小小的意外,拥有了变身成猫的能力。“一感到羞耻就变身?这就算了,我还能接受……”“可是为喵老是有母猫盯着我看啊!还有那只公猫,不许盯着我菊花看!”
  • EXO之忆初

    EXO之忆初

    一股口蘑中午摸起来我自己你利空空弄摸摸哦哦哦哦
  • 习惯正能量

    习惯正能量

    国外研究表明,一个人事业的成功与否20%与智力因素有关,80%与信心、意志、习惯、性格等非智力因素有关。其中,习惯占有相当重要的位置。从一个人的发展来说,习惯伴随着人的一生,影响着人的生活方式和工作方式。好的习惯是种正能量,也是能量的储蓄。培养好习惯,就是在为自己的未来贮存正能量。