1908] on Ice and its Natural History. 275 



I have attributed the presence of fragments of rock, whether 

 great or small, and to a considerable extent their rounded form, to 

 the chemical action of the moisture derived from the atmosphere. 

 Water penetrates, by its own weight, into any cracks or joints which 

 may occur in the rock, and into minute discontinuities of substance 

 by capillarity. It spreads and extends its decomposing influence 

 along the surfaces which lend themselves most readily to the process 

 of soaking. The warmer the rock is, the more energetic is the decom- 

 posing action. On the tops of high mountains rock surfaces, exposed 

 to the direct rays of the sun, acquire often, even in winter, a high 

 temperature, and when they are covered by snow, they are protected 

 from excessive cooling by radiation. All rocks have surfaces of rela- 

 tively imperfect continuity. These are found by water, which 

 enters easily provided the tem.perature of the surface of the rock is 

 not such as to convert it into ice. Far- spreading decomposition is 

 then only a question of time, and, after it has spread the falling 

 asunder of the parts of the rock under the influence of gravity is a 

 certainty. There is no necessity for assistance by any other agency. 

 The chemical action of atmospherie moisture and the tendency 

 of every part of a mountain or roek to yield to gravity when 

 not adequately supported, suffice to account for all the degra- 

 dation of roek which we observe. 



I liave not been able to discover the author of it, but it is a very 

 old and generally accepted doctrine, that the rock fragments which are 

 found so frequently covering the tops of mountains are split off from 

 the parent rock by the energy liberated by water freezing in its 

 interstices. I know of no detailed description of the process, nor 

 have I met or read of any one who has actually witnessed a rock being 

 split in this way. 



Discontinuities in the rock are postulated in order to admit the 

 water which is to be frozen, but no detailed specification is furnished 

 of how the opening is to be closed and the freezing is to be effected 

 after the water has entered. But it has been shown above that if 

 the water gains admission, it will in time disintegrate the rock by 

 chemical action, and gravity without assistance will complete the degra- 

 dation. Therefore freezing is unnecessary in order to account for the 

 facts. Moreover, the covering of a mountain top by fragments of its 

 own rock is a common occurrence in latitudes where frost is rare or 

 absent. 



In discussing the natural history of ice, it has been necessary to 

 some extent to include that of water and steam. In its physiographic 

 relations we have found that ice is as efficient a preserver of mineral 

 matter as it is of vegetable or animal matter in the everyday relations 

 of life. We have also found that the substance which chemists indi- 

 cate by the symbol HoO has the most destructive action on mineral 

 matter when it has passed from the gaseous state in the atmosphere 

 to the liquid state on the surface of the earth, and when this takes 



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