CLIMATIC AND QEOCHEMICAL BELATIONSHIPS 67 



It is to be noted, in the first place, that silica exists in 

 large quantities in the coastal plain soils, clue to the fact 

 that quartz is such a resistant mineral. The constant 

 washing that this soil has undergone has very largely 

 decomposed the silicates. The aluminium and iron are 

 rather low on the average in such soils, even in those of 

 the richer t^'^pe. It is to be noted also that the amounts 

 of phosphoric acid, calcium, potash, magnesia, and sodium 

 are much less in the marine soils, due to the excessive 

 washing that they have received. These figures would 

 lead to the belief that in general the marine soils are 

 lower in the mineral plant-food constituents than soils 

 formed in situ. The amount of organic matter that they 

 may contain depends entirely on their location and 

 climatic conditions. They may or may not be rich in 

 humus, according to circumstances. It is generally con- 

 sidered, however, that they are not so well supplied with 

 the organic elements as are other soils. 



53. Residual and glacial soils. — A comparison of 

 residual and glacial provinces cannot be made with such 

 assurance, because of the many kinds df rocks that may 

 have been parent to the soils and because of the great 

 variety of climatic conditions imder which the soil-form- 

 ing processes may have gone on. Such a comparison is 

 best made in a region where both residual and glacial soils 

 are found, as nearly as it is possible to judge, coming 

 from the same rocks. Analyses of soils under such con- 

 ditions are available, from the driftless and glaciated 

 parts of Wisconsin. The original rock was limestone. 

 The analyses ^ are as follows : — 



1 Chamberlin, T. C, and Salisbury, R. D. The Drift- 

 less Area of the Upper Mississippi. Sixth Ann. Rept., U. S. 

 Geol. Survey, pp. 249-250. 1885. 



