登陆注册
19468400000042

第42章

("Edinburgh New Phil.Journal" 1842 page 350.) clear description of the zoned structure of glacier-ice, far the most probable explanation of the laminated structure of these feldspathic rocks appears to be, that they have been stretched whilst slowly flowing onwards in a pasty condition (Ipresume that this is nearly the same explanation which Mr.Scrope had in his mind, when he speaks ("Geolog.Transact." volume 2 second series page 228) of the ribboned structure of his trachytic rocks, having arisen, from "a linear extension of the mass, while in a state of imperfect liquidity, coupled with a concretionary process."), in precisely the same manner as Professor Forbes believes, that the ice of moving glaciers is stretched and fissured.In both cases, the zones may be compared to those in the finest agates; in both, they extend in the direction in which the mass has flowed, and those exposed on the surface are generally vertical: in the ice, the porous laminae are rendered distinct by the subsequent congelation of infiltrated water, in the stony feldspathic lavas, by subsequent crystalline and concretionary action.The fragment of glassy obsidian in Mr.Stokes' collection, which is zoned with minute air-cells must strikingly resemble, judging from Professor Forbes' descriptions, a fragment of the zoned ice; and if the rate of cooling and nature of the mass had been favourable to its crystallisation or to concretionary action, we should here have had the finest parallel zones of different composition and texture.In glaciers, the lines of porous ice and of minute crevices seem to be due to an incipient stretching, caused by the central parts of the frozen stream moving faster than the sides and bottom, which are retarded by friction: hence in glaciers of certain forms and towards the lower end of most glaciers, the zones become horizontal.May we venture to suppose that in the feldspathic lavas with horizontal laminae, we see an analogous case? All geologists, who have examined trachytic regions, have come to the conclusion, that the lavas of this series have possessed an exceedingly imperfect fluidity; and as it is evident that only matter thus characterised would be subject to become fissured and to be formed into zones of different tensions, in the manner here supposed, we probably see the reason why augitic lavas, which appear generally to have possessed a high degree of fluidity, are not, like the feldspathic lavas, divided into laminae of different composition and texture.(Basaltic lavas, and many other rocks, are not unfrequently divided into thick laminae or plates, of the same composition, which are either straight or curved; these being crossed by vertical lines of fissure, sometimes become united into columns.

This structure seems related, in its origin, to that by which many rocks, both igneous and sedimentary, become traversed by parallel systems of fissures.) Moreover, in the augitic series, there never appears to be any tendency to concretionary action, which we have seen plays an important part in the lamination of rocks, of the trachytic series, or at least in rendering that structure apparent.

Whatever may be thought of the explanation here advanced of the laminated structure of the rocks of the trachytic series, I venture to call the attention of geologists to the simple fact, that in a body of rock at Ascension, undoubtedly of volcanic origin, layers often of extreme tenuity, quite straight, and parallel to each other, have been produced;--some composed of distinct crystals of quartz and diopside, mingled with amorphous augitic specks and granular feldspar,--others entirely composed of these black augitic specks, with granules of oxide of iron,--and lastly, others formed of crystalline feldspar, in a more or less perfect state of purity, together with numerous crystals of feldspar, placed lengthways.At this island, there is reason to believe, and in some analogous cases, it is certainly known, that the laminae have originally been formed with their present high inclination.Facts of this nature are manifestly of importance, with relation to the structural origin of that grand series of plutonic rocks, which like the volcanic have undergone the action of heat, and which consist of alternate layers of quartz, feldspar, mica and other minerals.

同类推荐
  • 陈刚中诗集

    陈刚中诗集

    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。
  • 权书

    权书

    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。
  • 重令

    重令

    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。
  • 法华文句记

    法华文句记

    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。
  • 理门论述记

    理门论述记

    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。
热门推荐
  • 天涯莫寻

    天涯莫寻

    ————————————————莫道欢未散寻途悲尽然——————————————————
  • 陶器、陶俑鉴赏及收藏

    陶器、陶俑鉴赏及收藏

    所涉及的鉴赏及收藏内容包括碑贴、鼻烟壶、古代茶具、古兵器、乐器、古代瓷器、古代家具、古代酒具、古代书画、玉器、古金银器、古钱币、古青铜器、古铜镜、古砚、银币、古董、钟表、古化石、画像石画像砖、甲骨、牙角器、偶像、连环画、名石、扇页、石雕、唐三彩、陶器、陶俑、铜鼓、图书、古代瓦当、文房四宝、印章、玺印、古今邮品 纸币、票券、珠宝、竹刻、木雕、漆器、紫砂等,介绍了与之相关的各种知识。图书内容翔实,通俗易懂,是广大古玩鉴赏及收藏爱好者的最佳入门书籍。
  • 青瞳之大容天下

    青瞳之大容天下

    这个男人,因为面容太清秀,每次带兵都会戴上面具;为了娶她,大战狼群,浑身上下伤痕交错;为了偷走她,不惜率兵奇袭她的国家;面对凶恶苍鹰,第一念头就是舍命护她周全……然而,互相伤害太重、错过了太多的两个人,牵手抑或放开,哪一个才是他们最好的结局呢?
  • 重生之巫毒神话

    重生之巫毒神话

    跳跃在亡灵上的舞蹈。行走于黑暗之中的巫师。刘潇面对背叛,爱情,绝望的时候选择了死亡。但是天不亡他,老天给了他重生的机会。刘潇带着前世亡灵巫王的记忆回到了12年前神话刚刚开始的时候,他运筹帷幄,善用人才。在这个神话世界中,刘潇怎么才可以立于不败之地。现实的仇恨,虚拟的成就,刘潇如何处理。最后巫皇的传说,会不会是刘潇的传说呢?
  • 异域法则

    异域法则

    他,本是天地造化的宠儿,天性无忧无虑。却不得不卷入一场六道混战,是否由他颠覆这个世界的法则,还是最终逃脱不了命运的枷锁。实力为尊,强者即为法则。世俗流言,人间乐土有座无量宫。得无量宫者得天下,六界疯狂。究竟是逆天神器,还是弥天阴谋?且看主角掀开六道下隐藏的面纱。..
  • 二月风

    二月风

    徐桂芳把10多万字的书稿,和她的名字,一并送到我的面前。要我审读,并求写序。三晋文化研究会正在编写《朔州通史》,10本,500多万字,无异于在修筑一段文化长城。我们几个人,日以继夜,尚感不及,岂敢顾左右言他?我迟疑了半晌。然而,还是接受了这道作业题。此类业余作业,几年来至少已有100家之多。回头看,确实耗费了我大量的时间和精力,但也深深地感谢青年朋友们,为我提供了一次又一次学习机会。
  • 猎心奇谈

    猎心奇谈

    或许冥冥之中自由天定,注定自己要亲手猎取他人之心,历经家人的离去、朋友的背叛、爱人的痛苦,才能明白“放下”二字。罗少东从未想过临安城会遭丧尸一劫,也从未想过这世间还有名唤平陵天荨的女子,更从未想过自己竟与神界四大剑神之首同一张脸。是上天的捉弄还是……
  • 悲情李陵

    悲情李陵

    仲秋,居延还感受不到肃杀的秋气。中午的阳光照在身上,依然火辣辣的。李陵从酒泉郡花城湖驻地出发,行军数十日来到了居延海。
  • 血花谣咒乱君心

    血花谣咒乱君心

    那一年,长安飞花满天,你与我向着不同的方向离去,你说,你手中所执之剑是为守护这瑶蓝国,你说,你不能因为儿女私情而放弃守护这天下,守护这黎明百姓,你终究还是为了这天下放弃我。那一年,你亲自送我上花桥,把我送到他的手里,你便这般狠心,独留我一人在这忍受孤独。在我生命绝望之时,你悄然出现在我的生命中,你的温柔,让我不自觉的沉溺在其中,当我满怀欣喜想和他过一生时,你却屠他满国,我成为你的皇后又能怎样,到最后我们的结局已被上天的注定,而我们都将孤独终老……
  • 星云剑祖

    星云剑祖

    家族被灭,为寻至亲之人,接触到自己从未接触过的世界。从此锋芒渐露,一路高歌踏天寻道,怒斩苍天。成就剑祖之名