SOILS. 11 



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ence between the upper and subsoil, the upper being mixed more or less with vegetable 



matter, besides being modified by atmospheric agencies. The broken and pulverized 

 material lying above the solid rocks is known to geologists by the general name of drift. 

 &quot;With respect to the origin of the agricultural soil, Prof. Agassiz says: 



&quot; There is hardly anywhere in the world an extensive tract of cultivated soil which 

 has not been brought to the place where it exists from considerable distances. It is no 

 doubt the case that the rocks are decomposing in places constantly; and the amount of this 

 decomposition is very great, varying according to climate, and is the result of influences which 

 are also different under different climatic conditions. In our colder northern regions the 

 decomposition is owing chiefly to the filtration of water into rocks, to the frosts following 

 that infiltration, to the splitting of the surface of the rock into fragments in consequence of 

 the expansion of frozen water, and thus the disintegration of the rocks themselves. In more 

 southern climates, where warm tropical rains are incessantly pouring upon the hard rock, it 

 is chiefly that agency and the decaying of the rock by the heat of the tropical sun which pro 

 duces a similar result. And yet this process, extensive as it is, is not the chief cause, hardly 

 an extensive cause, of the production of agricultural soil. There is another cause which 

 ought to be taken into account the wearing of the rock by the action of running water. 

 Here again we have an accumulation of an immense amount of loose materials which are the 

 result of the wearing action of running water. And yet even that is only a small portion of 

 the amount of loose materials which are scattered over the earth and form part of the agri 

 cultural soil. The main mass of the agricultural soil is derived from an entirely different 

 source, and is produced by an entirely different cause. There has been at work a grinding 

 machine more powerful than the action of the sun, of water, of frost or of wearing currents. 

 It is the agency of ice; and to that agency we owe not only the grinding of the rocks to 

 powder and all the comminuted material which forms the chief portion of the loose coatings 

 above the rocks which serve as the basis for our agricultural operations, but we owe also to 

 that natural machinery the mixture of rocks derived from different regions, which have 

 formed the compound coating over the whole surface of the earth, without which agriculture 

 would be limited to those regions the rocky foundation of which is such as to afford a suit 

 able soil. The agency of ice has been such as to bring together from remote countries the 

 loose materials from the limestone rocks, the slaty rocks, the marl beds, the granite rocks, 

 and the wearing of those materials into paste has transformed them into that coating which 

 really constitutes the bulk of our agricultural soil. Those materials have been remodeled 

 since by atmospheric agencies; they have been rained upon since the time they were deposited, 

 and of course the action of water has carried far off to other places what had been first 

 worked upon by ice. But this is not very extensive and does not constitute a part of the 

 primary formation of agricultural soil. 



&quot; It would lead very far to enter into an extended discussion of the manner in which ice 

 can have produced these results. It would probably excite a smile if I were to begin by 

 saying that the whole extent of the United States has at one time been covered with a sheet 

 of ice many thousand feet in thickness ; and yet geology can show that it was so. It would 

 probably excite doubt if it were stated that the whole sheet, moving from the north in a 

 southerly direction, has ground the loose materials resting upon the surface of the earth to 

 that paste which constitutes the agricultural basis; and yet it is so. It has been by a suc 

 cession of observations, starting from small beginnings, that this result has been reached and 

 is now recognized as a fact among geologists &quot; 



The Constitution and Texture Of Soils. Since soils are derived mainly from the 

 rocks, they will contain all the elements which the rocks originally did from which they were 

 formed ; usually, however, in different proportions, and in different chemical combinations, 

 and to this mineral matter is added various materials derived from the air (aside from the 



