452 



ORIGIN OF MUD -LUMPS AT 



[Ch. XIX. 



projected above low water 



Col. Sidell informs me, that 



made at Ne 



Custom House 



him 



lump ■ * and no doubt many such would be found in the older 

 parts of the delta, and they would present a very perplexing 



geologist who had no clue to their mode of 



enigma 

 origin 



to a 



We 



matter disengaged from cracks in these newly-raised islands, 



almost 



a successful Artesian boring has been made, the water at 

 first spouts up to a height far beyond that to which it would 

 be carried by simple hydrostatic pressure. A portion of the 

 propelling force usually consists of atmospheric air and car- 

 bonic acid gas, which last is generated by the decomposition 

 of animal and vegetable matter. Of the latter there must 

 be always a great store in the recent deposits of a delta like 

 that of the Mississippi, as they enclose much drift timber at 

 all depths, and the pent-up gaseous matter will be ready to 

 escape wherever the overlying impervious clays are upheaved 



I am informed by Col. Sidell, 



and rent. 



>/ 



that when one of the lumps was blown up with gunpowder, 

 a great ebullition of gas, chiefly carbureted hydrogen, took 

 place, and left a crater-shaped hollow. Such gas has also 

 been known to be given out for several years m succes- 

 humi ; from which facts the Colonel infers, that when it 

 cannot get vent it may sometimes accumulate to such an 



sion 



come 



cumbent mud, and force it up in the shape of a mud-lump. 

 But this hypothesis leaves unexplained the important mcx 

 that the swelling up of the bottom always takes place on 



what are called 'the passes,' or 







off the extremity of the 



delta, near those points where the chief load of fresh sand, 

 gravel, and sediment is thrown down on the muddy bottom 

 of the gulf. The decay of drift timber and other vegetable 

 matter must be going on actively at various deptlis au 

 over the delta, and often far from the river's moutn , 



>- 



* Letter to the Author, Oct. 16, 1805. 



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