240 THE POPULAR SCIENCE MONTHLY 



vex form of the delta protrusion; nor why there should he the sudden 

 diversion of the several main distributaries from one permanent point, 

 viz., the Head of the Passes, and a failure of the Passes themselves to 

 give out numerous minor distributaries, as is the case in all other 

 known deltas. 



Moreover, the existence of the " Neck," a single, narrow-banked 

 channel carrying the main river from below Forts Jackson and St. 

 Philip to the Head of the Passes without breaking through the narrow 

 embankment into Grand and Bird Island Bays, is precisely analogous to 

 the fingers of the lower delta. 



MuDLUMP Clay 



Even a cursory examination of the material causing this division 

 and obstinately resisting the impact of the main current of the river at 

 the Head of the Passes, shows that it is wholly distinct in character 

 from the ordinary sandy and silty river sediment, and very different also 

 from the Port Hudson clay; being a compact, impervious gray clay, 

 and corresponding exactly to the material constituting the mudlumps. 

 So long as it remains submerged or fully wetted, this clay resists ero- 

 sion to a remarkable degree. 



As we descend either of the Passes, an examination of their banks 

 shows that these are formed of this same gray clay, and not of sandy 

 or silty river deposit, which usually covers the clay only to the depth of 

 a few feet. Hence, even a rise of the river does not wash out such 

 lateral channels as Chamberlin and Salisbury speak of, connecting the 

 river current with the adjacent bays. Even where such channels exist 

 they have occasionally to be dug out by hunters or fishermen in order 

 to reach the intervening bays, as they tend to fill up with the debris 

 of mudlumps, and with river deposit. As we approach the mouths of 

 the Passes, the banks are found to consist of small islets with small, 

 shallow channels between, which, however, are also being rapidly filled 

 in, progressively, partly by river deposit, but chiefly by disintegrated 

 clay of the mudlump masses that have been raised above the water 

 level. For when this clay of which the mudlump masses consist has 

 been exposed to repeated partial drying and wetting, it crumbles into 

 a loose mass, which is washed by rains into the shallow channels inter- 

 vening between the mudlump islets and there settles into a mass very 

 resistant to erosion. 



Active Mudlump Coxes 



Still farther downstream we come, in all hut the South Pass, to 



mudlump islets obstructing the channel, historically known to have 



been upheaved from the river bottom, and frequently exhibiting low 



cones from the apices of which there is a steady flow of semi-liquid mud, 



