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风化与土壤

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  The principal significance of the different climatic types to the student of geology lies in their influence on soil formation and on erosion. Each climatic environment places its own stamp upon the soils developed there, and each influences, through its control over vegetation, amount of rainfall, and evaporation losses, the geological processes involved in molding the details of the earth’s surf ace. Erosion, the process of removal of rock waste, will be discussed in later chapters5 here, we will examine the influence of several different climatic environments upon the weathering of different rock types. 对于学地质的人来说,各种不同气假.类型的重要意义,就在于它们对土壤形成和侵蚀所产生的影响。每种气候环境,对该地发育的土壤都留下了自己的痕迹;同时每一种气候环境,通过 它对植物生长、降雨量和蒸发量的控制,影响着与塑造地表细微 外形有关的地质作用。侵蚀作用,也就是岩屑的迁移作用,将在后面几章中讨论。这里,我们来研究一下几种不同的气候环境对各类不同岩石的风化作用所产生的影响。 -The most familiar example of weathering is the etching and discoloration of the surface, of an unpainted board left out-of-doors. Rock, exposed on the earth s surface, also decays and leaches, but much more slowly. If the product of rock decay is merely broken and discolored, it is called mantle rock 5 but if it is loose and porous enough for plants to find a foothold, it is called soil?.
 
  人们最熟悉的风化作用的例子,就是一块放在户外、未经油漆的木板表面发生的刻蚀和褪色现象。岩石如果暴露在地表,也 会遭到腐蚀和淋滤, 只不过进程缓慢得多。如果岩石的腐蚀产物仅仅是破碎和变了色,就叫做风化层I如果它疏松多孔,植物能 植根其中,就叫做土壤。
 
  Soil is more common than rock at the earth's surface. Almost all outcrops of rock are less firm-more easily crumbled and broken-than is the same rock at a depth of 20 or 100 feet?. Many rocks that are. black or steel gray where penetrated in mines, wells, or deep quarries are yellow or brown in outcrops. In some, the yellow color is a mere stain on or near cracks, but in others it is more pervasive and is accompanied by drastic changes in mineral composition of the rock. That the changes result from weathering is shown by observations on building stones?. For example, the exposed faces of the sandstone used in the older buildings at Stamford University turned yellow in 5 to 10 years, and, where exposed to repeated wettings, began to crumble in 20 to 30 years.
 
  在地表,土壤比岩石更为常见。几乎所有的岩石露头,都不如20-100英尺以下的同种岩石坚固,而是比较易于破碎。许多岩石在矿井、钻井和深采石场里为黑色或铁灰色,而在露头上则 呈黄色或褐色。有的岩石,仅在裂纹上或裂纹附近染成黄色;但是,在另一些岩石中,黄色则扩散较广,而且伴随发生了岩石矿物成分的强烈的变化。对建筑石料进行观察,就会发现这种变化 是由风化作用引起的。例如,斯坦福大学一些比较古老的建筑物 所使用的砂岩,其暴露面在五到十年内变成黄色,而经常处于潮湿状态的暴露面在二十到三十年内开始破裂。
 
  
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