MASSACHUSETTS PE.\T LANDS 37 



to circumstances through adjoining sandy areas. It is well known 

 that much of the dissolved constituents from the upper soil layer 

 is carried down by the seasonal rainfall and is commonly redeposited 

 some distance below the surface soil, forming the " pan." The upper 

 sand layers are then white or grey in color and very silicious, and 

 where a surface layer of peat or humus is absent, the vegetation 

 becomes more and more open, and dwarfed and heath-like. The 

 land approaches the character of a "barren," since only plants 

 with a shallow root system and with a low requirement of nutrition 

 and growth appear to be able to thrive and mature. 



With free drainage at deep levels, pan formation is rarely found. 

 Investigations of European writers have shown how far-reaching 

 is the influence of washing-out or leaching-out of the soluble con- 

 stituents of the soil in climates of abundant seasonal rainfall. 

 They have pointed out the desirability of avoiding fallows as much 

 as possible, and of keeping the soil well occupied by crops, particu- 

 larly hay and pasture grasses, certain staple crops, and root crops. 



In the cases where seepage and ground water are not carried 

 away by free drainage, the leached materials tend to accumulate 

 in the soil and to cement the sandy substrata. During the drier 

 season of the year the downward movement of water ceases; the 

 groundwaters from the lower layers begin to move upward, and 

 the soluble materials have then an upward tendency. 



Periods of drought, strong winds, and consequent evaporation 

 favor absorption and the deposition and concentration of iron and 

 other salts in solution. The loss of any excess of carbonic acid 

 from the underground waters, the presence of alkaline earth, or a 

 substratum richer in soluble salts; the increased oxidation in the 

 stratum on being exposed to the atmosphere, and the destruction 

 of the colloidal humus complexes, which is parti}' accomplished 

 by the action of bacteria, — any one or all of these factors may 

 liberate the iron, alumina, magnesia, and others. These may 

 form under certain conditions either nodules or concretions in the 

 soil, or in some cases a continuous layer of considerable thickness. 

 The solid aggregations vary widely in composition, in amount of 

 fine-grained organic matter and in degree of cementation. Hence 

 much importance should be attached to the character and color of 

 peaty waters, the amount of suspended material which they con- 



