and the Mudlumps of the Mississippi. 3(U 



agged outlines, whose disintegrated materials are rapidly yieid- 

 ng to the combined attack of rain, sunshine aad wave's, till 

 ■omething looking like a large stump of a tree is all that re- 

 nains of an island of several acres ; and finally the shoal, marked 

 n-'laiigerous rollers, whose surface, on a calm day, still exhibits 

 !i<> concentric markings corresponding to the several cones 

 •'-''•''. '"originally built up the island. 



' -i-et being unable at the present time, to present a 

 -of the ' ■ "'■■' 



1857. 



Nascent Lumps. — As regards the first, it is probable that a 

 good many lumps never pass beyond that stage of develop- 

 ment, for the reason that, so soon as the resistance is materially 

 increased by the emergence of a portion above the surface of 

 the water, the upheaving force seeks a vent elsewhere. 



Either the mud or gas-spring breaks out beneath the water, 

 ;htI l)ecomes perceptible only by the more or less regular and 

 localized evolution of bubbles on the outskirts of th'e lumps ; 

 a very common phenomenon in the neighborhood, not only of 

 pew and active lumps, but also about extinct ones, which" are 

 m course of demolition bv the waves. On the extensive sand v 

 shoal off Stake Island, on the Southwest Pass, such subaqueoii- 

 gas-springs may be observed in great numbers.— Or it ni;,\ 

 iiappen, that another portion of the bottom, now offering h-' 

 resistance than the mudlump, will, in its turn, give way bef )i' 



He upheaving force, till the same degree of emersion is ob- 

 tained, or a vent is opened. 



. -I have been unable to ascertain how high any mudlumps can 

 rise bodily above the water without the appearance of a vent. 

 As much as three feet has been observed with certaintv; but 

 unless the fact that it is a new upheaval be historicallv known, 

 " must be extremely difficult to ascertain it, unless, by actual 

 access to the interior, it can be shown that its surface strata are 

 ow nver deposits, which can readily be distinguished from 

 ^nose formed by mudlump vents. Yet these might, during the 

 « evatiou of the lump, have been removed by the current At 

 ^ events, I have failed to find on the surface of any lump 

 °^^cli above tide-water, anything like true river alluvium ; the 

 ^^ible material being either such as is now formed by active 

 from +1?^' (as on the lower slopes), that which obviously results 

 01 the disintegration of the former, being altogether devoid 

 "I structure. 



bar^ ^^ ^^^^ *^^^ lumps sometimes sink from view again after 

 e emergence. I know of no authentic example, but it 



