GEOLOGICAL CLASSIFICATION OF SOILS 53 



material, age, and climatic conditions. There are great 

 tracts of general farming land, besides wide areas of special- 

 purpose soils adapted to highly specialized industries. The 

 latter soils require refined and intensive methods of culti- 

 vation. Except for certain areas the coastal plain soils are 

 well aerated and easy to cultivate. Except in the lower 

 coastal plain belt they are well drained. Severe leaching as 

 well as serious erosion occurs in times of heavy rainfall. 

 When sufficiently supplied with organic matter, carefully 

 fertilized, and cultivated properly, these soils support a great 

 variety of crops such as cotton, maize, oats, forage crops, 

 and peanuts, besides vegetables and fruits of many varieties. 

 30. The ice age and the American ice sheet. 1 — If in any 

 region the temperature and snowfall stand in such rela- 

 tionship that the heat of summer does not offset the winter's 

 accumulation of snow, great snowfields form. If this con- 

 dition persists year after year the temperature is reduced 

 to such an extent as to increase the proportion of the snowfall, 

 which escapes the summer heat. The pressure of overlying 

 snow and the influence of the summer melting soon change 

 the snow into ice with a complicated recrystallization. As the 

 depth of the accumulation increases outward movement is 

 inaugurated due to the strong lateral pressure. As the ice 

 moves slowly forward under this tremendous pressure, with 

 an almost incredible thickness and a plasticity which ordi- 

 nary ice does not possess, it conforms itself to the uneven- 

 ness of the areas invaded. It rises over hills and shapes 

 itself to valleys with surprising ease. Not only is the exist- 

 ing soil mantle swept away by such an invasion but the 

 underlying rocks are ground and gouged. When the ice 

 melts back and the region is again free a mantle of soil ma- 

 terial remains. 



*For a complete discussion of glaciers and glaciation, see Salis- 

 bury, R. D., The Glacial Geology of New Jersey; Geol. Survey of 

 New Jersey, Vol. 5, 1902. 



