





)*\ 





: 



''Mat 



.r. 

 ^position 



Ita life 

 iinber i 







r lit 

 iipheaT 





L Sid 



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y 







lias alii' 

 n bo 



• 



Ch. XIX] 



THE MOUTHS OF THE MISSISSIPPI. 



4 5 3 



that it seems to me more probable that the gaseous ema- 

 nations play only a secondary part, helping to bring up 

 mud from below and deposit it on the slopes of the newly 



raised mound, 



mud 



The 



initiatory moving power may probably be derived from the 



wn 



mulated during the flood season off the various mouths or 

 passes, upon a yielding bottom of fine mud and sand. This 



new deposit, 



Messrs. H 



and Abbot, 



forms annually a mass of no less than one mile square, 

 having a thickness of twenty-seven feet. It consists of mud, 

 coarse sand, and gravel, which the river lets fall some- 

 what abruptly when it first comes in contact with the still 



salt water 



of the gulf. 



A cubic mass of such enormous 



volume and weight thrown down on a foundation of yielding 

 mud, consisting of materials which, as being very fine and 

 impalpable, had long before been carried out farthest from 

 the land, may well be conceived to exert a downward pres- 

 sure capable of displacing, squeezing, and forcing up laterally 

 some parts of the adjoining bottom of the gulf, so as to 

 give rise to new shoals and islands. 

 Eailway engineers are familiar with the swelling up of a 



mor 



embankment 



I saw an 



example of this in the year 1839, in the Loch of Eescobie, 

 in Forfarshire, five miles east of the town of Forfar. That 

 lake had been partially drained, and the railway 

 was carried over newly-exposed, soft, and swampy 



moun 



mound 



which gave way so as to let the 

 feet. It then became necessary to pile up additional matter 

 fifteen feet thick in order to obtain the required level. On 

 one side of the embankment, the bog, when I visited the 

 place, had swollen up in a ridge 40 feet long and 8 feet 

 high, the upper portion consisting of peaty matter traversed 

 by numerous willow roots. In the highest part of this 



mass 



their greatest width, and open for a depth of two yards or 

 more. On the opposite side of the railway mound, and about 

 100 yards distant from it in the middle of what remained 



