GEOLOGICAL CLASSIFICATION OF SOILS 55 



from New England to the Pacific coast (see Fig. 4). 

 They comprise a great variety of soils, not only as to their 

 physical character, but also as to fertility. They are 

 adapted to many crops, but general farming is practiced 

 on them to the greatest degree. This means extensive, 

 rather than intensive, operations. In some localities 

 dairying has been developed to a large extent, and has 

 proved to be not only a means of obtaining paying re- 

 turns from such soils, but at the same time a method of 

 keeping up their fertility. 



42. Glacial lakes. — Such great masses of ice could 

 not advance and retreat, again and again, on such an 

 extensive scale, without causing the formation of great 

 torrents of water. It is more than probable that at all 

 times great streams gushed from the ice front, laden 

 with much sediment. Often these streams were under 

 pressure, which when released caused an immediate 

 deposition of material. As long as the ice front stood 

 south of the east and west divide, this water found ready 

 egress and flowed rapidly away to deposit its load as 

 gravelly outwash, river terraces, valley trains, and allu- 

 vial fans. These formed alluvial soils of varied character, 

 depending on the size of the materials carried. There 

 came a time, however, in the retreat of the ice, when the 

 front stood north of the divide and only a small pro- 

 portion of the water found itself free to flow over the divide 

 and away to the southward. The remaining ftvater was 

 ponded between the ice front and the old divide. Thus 

 glacial lakes were produced, of large or small extent, 

 according to the position of the ice. The location of 

 such lakes is shown on the soil map of the United States. 

 The ponded water remained in this condition for many 

 years, subject, of course, to changes concordant with 



