and the Mudlumps of the Mississippi. 359 



The mudlumps originate in upheavals of the bottom, in the 

 region lying between the extreme point of the mainland and 

 the crest of the bar, at the main outlets of the passes. They 

 all lie within a distance of from one to three miles from the 

 axis of the main current, and nowhere extend into the bays in- 

 tervening between the several active mouths. The pilots are 

 under the impression that they form more frequently in the 

 main channel than elsewhere ; but allowance must be made for 

 the natural infrequency of their observations outside of the latter ; 

 so that only the more obvious and remarkable changes of the 

 bottom, when occurring outside of their regular range, would 

 be likely to come under their notice. A priori^ it would seem 

 probable that inasmuch as the resistance to the upheaving force, 

 other things being equal, must be less in deep than in shallow 

 water, the lumps would rise more frequently and more rapidly 

 in the channel than elsewhere. On the other hand, the denu- 

 ding force of the river current must greatly diminish the chan- 

 ces of any such upheaved mass appearing above the surface, or 

 even becoming manifest by a diminution of depth, when pro- 

 gressing slowly. "Weighing these considerations against each 

 other, I think a balance remains in favor of the pilot's opinion ; 

 the more as concurrent testimony goes to show that whenever 

 the channel is changed, either by the accumulation of deposit or 

 the interference of a mudlump upheaval, the old channel is 

 promptly occupied by mudlumps throughout the abandoned 

 portion. 



As regards the rapidity of the upheaval, it appears to vaiy 

 irom an almost secular rate, to that of several feet in 24 hours. 

 It has been rumored that lumps had been seen to rise visibly, 

 and burst open like a bubble, but I have been unable to trace 

 the statement to any reliable source, and it is discredited by the 

 pilota The most rapid rise of which I have obtained reliable 

 information was witnessed by Capt Andrews, of New Orieans. 

 4j states that a steamer having run aground about nightfall in- 

 side the bar, her bow being on a mudlump in about 2^ feet of 

 J^ater, he towed her off during the night, and in the morning 

 round the imprint of her bow 18 to 24 inches above water, in the 

 sott mud. Allowing for the possible maximum influence of 

 tides m favor of the difference observed, the minimum rate of 

 JJPheaval, according to these data, still amounts to one inch per 

 ^our. Nor is this the only case in which a rapid shallowing of 

 tne water has been observed as a consequence of the grounding 

 01 large vessels. This has usually been ascribed to the accu- 

 mulation of deposit in the slack water so formed, and in many 

 distances this may have been the true cause. But this explana- 

 tion can hardly apply to the case detailed above, and it is rea- 

 sonable to suppose that the shock of a grounding vessel may 



