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
  • 海道经

    海道经

    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。
  • THE OLD CURIOSITY SHOP

    THE OLD CURIOSITY SHOP

    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。
  • 佛说难提释经

    佛说难提释经

    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。
  • 郡斋读书志

    郡斋读书志

    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。
  • 众仙赞颂灵章

    众仙赞颂灵章

    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
  • 错的时间错的梦

    错的时间错的梦

    风像羽翅尖撩过大海,泛起无声的涟漪晃荡。你身着金光四射的衣裳,裙袂摆动过我心上。
  • 国际经济法作业集

    国际经济法作业集

    为更好地配合《国际经济法》课程的教学, 方便学生更好地学习国际经济法律、法规的相关知识, 结合《国际经济法》教材所涉及的相关理论和实际问题, 我们编写了本作业集。在编写过程中, 力求在把握国际经济法基本体系的基础上, 密切联系国际经济贸易法律事务, 将学术性与应用性融为一体, 以满足对学生知识结构的要求。
  • 记忆零星

    记忆零星

    很多年前只要一抬头就可以看到满天的星星,而现在天空却成了零星点点,甚至无影无踪。我从小就是一个很多愁善感的人,是一个会抬起头仰望天空的自卑男孩,当我敲起键盘的时候,似乎所有的画面都在脑海中盘旋,一幕幕地跳跃在我的瞳孔里面,像零星般聚合,渐渐点亮了夜空……
  • 天堂向左,深圳往右

    天堂向左,深圳往右

    一个乞丐说:这里冬天不冷,真好。一个民工说:工资高啊,我干了四年,在老家盖了一栋楼,人人都以为我发了财。一个坐台小姐说:陪聊三百,过夜一千五,等我妹妹大学毕业,我就不干了。一个白领说:我来了六年了,供了一套房,压力不小,只想找一份安安稳稳的工作。一个老板说:钞票决定一切。没有钱就没有生活。鹏鸟的故乡。梦想之都。欲望之渊。爱无能的城市。沦陷的乌托邦。失去信仰的耶路撒冷。然后,一切比喻都没有意义。原来它只是你的一个影子。
  • 田家五行

    田家五行

    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。
  • 闪耀传奇

    闪耀传奇

    王浩,从一个默默无闻的孩子,直到成为一方豪杰。从中那些坦途那些岁月,那些无法磨灭的兄弟情义。他说,我这一生,活一口气。
  • 血瞳女孩

    血瞳女孩

    如果,你的学校曾是乱葬岗。如果,你半夜里起来上厕所。如果,你觉得脖子凉飕飕的。如果,你想回头看个究竟,那么恭喜你,你会发现你背后多了一个流着血泪的女人,而你的头部正被马桶内伸出的一只小手一点点拉进马桶直至死亡....血瞳女孩冷嫣,天生一双骇人的血色双瞳,能看见一切凡人所不能见的东西,比如鬼。
  • 路西法

    路西法

    走近三界最强中二青年的叛逆人生!以百分之二百的理想主义谱写而成的黑暗圣经!关于自由与信仰的终极解答!人世间有许多不公平,许多人会这样安慰自己,但路西法不会。世界错了,他就要去纠正这个世界。
  • 甜蜜糖果:太爱你的微笑

    甜蜜糖果:太爱你的微笑

    “叶子,我的初吻你不可以抢!”文晴晴瞪着一个足足比她高两个头的男生霸道的下达命令。“晴晴,可是我觉得男生先吻比较霸气哎~”叶俊森不得不低头看着这个矮子,一脸的无奈。“你说什么?再说一遍”文晴晴斜着眼睛藐视着叶俊森。“好,遵命”叶俊森行了个军礼,吃瘪的样子让文晴晴忍不住大笑……
  • 巨人神话:史玉柱

    巨人神话:史玉柱

    本书从史玉柱的个人特性出发,把他出道以来的成功得失与他的性格成长结合起来进行了深入分析。