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.
對于學地質(zhì)的人來說，各種不同氣假.類型的重要意義，就在于它們對土壤形成和侵蝕所產(chǎn)生的影響。每種氣候環(huán)境，對該地發(fā)育的土壤都留下了自己的痕跡；同時每一種氣候環(huán)境，通過 它對植物生長、降雨量和蒸發(fā)量的控制，影響著與塑造地表細微 外形有關(guān)的地質(zhì)作用。侵蝕作用，也就是巖屑的遷移作用，將在后面幾章中討論。這里，我們來研究一下幾種不同的氣候環(huán)境對各類不同巖石的風化作用所產(chǎn)生的影響。
-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?.
人們最熟悉的風化作用的例子，就是一塊放在戶外、未經(jīng)油漆的木板表面發(fā)生的刻蝕和褪色現(xiàn)象。巖石如果暴露在地表，也 會遭到腐蝕和淋濾， 只不過進程緩慢得多。如果巖石的腐蝕產(chǎn)物僅僅是破碎和變了色，就叫做風化層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，土壤比巖石更為常見。幾乎所有的巖石露頭，都不如20-100英尺以下的同種巖石堅固，而是比較易于破碎。許多巖石在礦井、鉆井和深采石場里為黑色或鐵灰色，而在露頭上則 呈黃色或褐色。有的巖石，僅在裂紋上或裂紋附近染成黃色；但是，在另一些巖石中，黃色則擴散較廣，而且伴隨發(fā)生了巖石礦物成分的強烈的變化。對建筑石料進行觀察，就會發(fā)現(xiàn)這種變化 是由風化作用引起的。例如，斯坦福大學一些比較古老的建筑物 所使用的砂巖，其暴露面在五到十年內(nèi)變成黃色，而經(jīng)常處于潮濕狀態(tài)的暴露面在二十到三十年內(nèi)開始破裂。
