,CH. II] The E feet of Past History 19 



or were carried only short distances: sometimes they 

 were carried away a great distance. In many districts, 

 as in Central and Eastern Europe, parts of Asia and of 

 the Middle West of the United States {e.g. in Nebraska), 

 wind was the transporting agent and the soils thus 

 formed, known as loess soils, are remarkable for the 

 narrow range of variation in size of their particles, the 

 wind only being able to carry particles of certain dimen- 

 sions. Over much of England north of the Thames, and 

 the northern parts of the United States, glaciers carried 

 the particles to their present position, grinding them 

 sometimes almost to impalpable powder. Elsewhere 

 flowing water was the transporting agent. From the 

 moment the original rock solidified right down to the 

 present day the particles have been subjected to all 

 those influences of rain, frost, heat and water that are 

 collectively summed up in the term chmate. The par- 

 ticles as we find them to-day are largely the result of the 

 conditions through which they have passed. The past 

 history of the soil has had an enormous effect on its 

 present character, indeed in many cases the properties 

 of the soil were largely settled in geological ages far re- 

 mote from our own. Thus the red Triassic soils formed 

 mainly under continental conditions with much wind- 

 drifted material are quite distinct in character from the 

 poor clays of the coal measures that preceded them or 

 the grey soils of the succeeding Lias : all these differ con- 

 siderably from the Oxford Clays and these in turn from 

 the Weald Clays. 



The rock from which particles originally sprang has 

 also determined the character of the soil. One of the 

 commonest mineral substances on the earth is silica, the 

 chief constituent of quartz, flint, and sand. In these 



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