506 SOILS. 



Lowland Tree Growth. The variations occurring in the val- 

 leys or alluvial bottoms are less obvious to superficial observa- 

 tion, yet equally important and cogent to the close observer. 

 In the properly alluvial lands, one dominant condition, that of 

 adequate moisture supply, is almost always fulfilled, irrespec- 

 tive of soil quality. In addition to this, as stated in chapter 

 2 (see page 24), practically all the alluvial lands of the 

 humid region may be considered as being of a more or less cal- 

 careous character, as compared with the adjacent uplands. 

 These two important conditions dominate in a great measure 

 the minor ones of variation in soil-texture. Yet where, as 

 is largely the case in the southern part of the State of Missis- 

 sippi, the amount of calcic carbonate is insufficient to overcome 

 the sourness of the soil, the vegetative contrasts become ex- 

 tremely striking and characteristic, as explained above. 



Contrast Between " First " and " Second " Bottoms. A 

 very striking phase of transition between the alluvial bottoms 

 and the uplands proper in the Cotton States are the second bot- 

 toms or hammocks of the streams, whose soil and tree-growth 

 in most cases differ markedly from those of the first bottom ; 

 and these being usually closely adjacent, often afford a very 

 striking contrast to the latter. From some antecedent geologi- 

 cal cause not fully understood, these hammocks, usually ele- 

 vated from 4 to 10 feet above the present flood plain, have 

 almost throughout soils of a fine sandy, pulverulent or silty 

 nature, frequently in strong contrast to heavy clay soils in the 

 first bottom. 



They seem, moreover, to have been at some time subject to 

 prolonged maceration under water, resulting in the reduction 

 of the ferric oxid, and its accumulation in the lower portion 

 of the deposit in the form of bog-ore spots or " black gravel." 

 Since such a process always results in the abstraction of phos- 

 phoric acid from the general mass of the soil, to be accumulated 

 in the bog ore in an inert condition, 1 these hammock soils, 

 usually whitish or gray in color, are almost throughout poor 

 in phosphates as well as in lime; the latter having been defini- 

 tively leached out. The resulting vegetation, as may be 

 imagined, is widely different from that of the bottom proper, 



1 See Chapter 2, p. 24. 



