BLACK WATERS. 365 



extent in most of the counties on our tide-water rivers, as most of 

 them have poor forest lands and some swampy streams in the 

 interior. 



As the opposite circumstances of the presence or absence of 

 colour in different waters is certainty not caused by such difference 

 in the sources of supply, they must be caused by some subsequent 

 action, which serves to clear the waters in one locality, by combin- 

 ing with and taking off the dissolved colouring matter, and which 

 action does not take place elsewhere, because there is no such 

 efficient agent present. That agent I take to be carbonate of lime, 

 or some other salt of lime in the soil in the one case, and which is 

 present in quantity altogether insufficient for such action in the 

 other case. According to the views which were presented (page 

 96) in regard to the power of calcareous earth to combine chemi- 

 cally with vegetable matter, if the coloured waters should flow over 

 soils furnished with calcareous matter, or into streams impregnated 

 with any salts of lime, it would follow that the suspended or dis- 

 solved vegetable extract would combine with the calcareous matter 

 of the soil in the water, and the new combination be precipitated, 

 and be given to the soil, as manure, either immediately or remotely. 

 This effect would be greatly aided if the streams swollen by rains 

 actually passed in contact with and washed away exposed banks of 

 marl. All recent rain-water contains a small amount of carbonic 

 acid, and that impregnation enables water to dissolve a proportional 

 quantity of carbonate of lime, which is insoluble in water without 

 this addition of carbonic acid. Therefore, in such circumstances 

 the swollen streams and land floods would necessarily dissolve some 

 carbonate of lime, which would be thus placed immediately and 

 fully in mixture and perfect contact with the before dissolved vege- 

 table colouring matter, and next must take place the combination 

 of the two, and precipitation of the compound manure. The con- 

 sequence must be, that the lands thus overflowed must be more or 

 less enriched by every heavy rain ; while the lands overflowed by 

 the coloured waters receive, or retain, nothing of soluble vegetable 

 matter from this source, and may even lose part of what they had 

 before received from the decay of their own growth, or other 

 sources, by its being dissolved and carried off by such overflowing 

 waters. 



Now let us see how the actual results agree with these different 

 causes, so far as the causes are known to exist. In the limited 

 region particularly referred to above, the low grounds, subjAt to 

 inundation by rains in a state of nature, and having beds of marl 

 which the stream cuts through, are of much richer soil than any 

 others, though the quantity of marl displaced by the stream (if in- 

 deed any such displacing be perceptible) would seem altogether too 

 small in amount to produce such extent of fertilization by direct 

 31* 



