370 CONFINED TO ACID SOILS. 



cate more of lime in the soil; and, according to my views, also the 

 inability of water to become black, or at least to remain coloured.* 



The waters of Black water river aiid its tributary streams and 

 swamps become darker in autumn, owing to the low level of the 

 surface at that season. This is according to sound reason ; as eva- 

 poration of the solvent fluid necessarily increases the strength of 

 the solution. But this cause is held by most persons as secondary 

 in force to another, viz. : the dropping of the leaves, and especially 

 of the numerous black-gum trees, and their berries, at that season, 

 on the swamps and in the streams. Of course such v is the source 

 of the colouring matter ; but it would produce no notable or abid- 

 ing effect, but for the want of lime both in the soil and in the wa- 

 ter. The extensive tide swamps on the creeks of James river, are 

 covered with a dense growth of trees, of which a large proportion 

 are black-gums. Yet in the numerous rills trickling or oozing out 

 of these soils, after some days of low tides, I have never observed 

 the water to be dark, or in the least discoloured. Yet the soil of 

 these tide swamps is as much of vegetable formation as any capa- 

 ble of bearing trees, and is believed to be more so than the swamp 

 lands of Blackwater river and its tributaries. Therefore it is not 

 the abundance of dead vegetable matter in a soil, nor the quantity or 

 kind of leaves furnished by the trees growing on it, which alone or 

 together produce coloured waters. The earthy portion of the soil 

 of these tide marshes and swamps, small as is its amount, is not 

 acid, but neutral, and the lime contained serves to prevent the wa- 

 ter remaining discoloured. 



Yet this is not always the case on tide swamps. The waters of 

 Pocomoke river, flowing into the Chesapeake, are black, which I 

 presume is owing to the deficiency of lime in the water and in the 

 surface soil of the lands from which the waters flow. 



The great Dismal Swamp of Virginia and its lake, and the still 

 more extensive swamps and lakes of North Carolina, all present 

 black waters, and which may all be accounted for by the reasons 

 Here given. 



Neither is it necessary that marl beds should be wanting to pro- 

 duce the effect of black waters. It is only necessary that the marl 

 (no matter how abundant) should be so far below the surface as 

 not to affect the overflowing waters, and that the soil of the higher 

 lands should be generally of acid quality. Such are the lands on 

 Blackwater river and its tributaries. And though marl was scarcely 



* The extract translated from M. Puvis' "Essai sur la Marne," and intro- 

 duced at page 150 of this essay, affords testimony that the facts in regard 

 to the existence and localities of black waters in France accord strictly 

 with the views presented in this article. This writer says that, "during the 

 month of August, the water of the ponds on calcareous soil does not be- 

 come blackish, as often happens in silicious ponds." 



