366 E. W. Hilgard— Geology of the Delta, 



passing tliroagh a variety of middle stages in which it strik- 

 ingly resembJes masses of trap or basalt, magnified into distant 

 mountains by the peculiar optical delusion prevaihng in the 

 region,* is finally reduced to what, at a distance, appeai-s to be 

 the stump of a tree. At last, some storm sweeps away this last 

 monument of the disappearing lump, and white-capped rollers 

 alone mark, thereafter, the higher points of the mud-shoal. 

 I have best observed these phenomena of disintegratin: ' 



3n to perfection, 

 no mudlumps off South Pn-^- 

 G-raud Bayou ; a statement which may require to betaken with 

 a grain oi' allfiwaiice, but agrees with the general impression 

 thit the mouths discharging the largest amount of water, also 

 exhibit mudlump activity on the most extensive scale. 



The Southwest Pass is the main outlet at the present time : 

 the area inside the bar is thickly studded with mudlumps, 

 chiefly west of the channel ; and as before stated, lumps have 

 risen there repeatedly under the eves of the pilots and survey 

 parlies. Yet there is not there, at the present time, a single 

 aciire cone, so far as I am aware ; although salt v^ater and gas 

 s})rings are of frequent occurrence, both on and around the 

 islands. There is a marked difference between the river 

 de[v>sits as well as the mudlump materials of Passe a I'Outre 

 and Soutliwest Pass, the latter being decidedly more sandy. 

 and sand bars taking the place of the mud flats off the former. 

 Whether this circumstance (the natural result of the greater 

 swiftness of the current in Soutliwest Pass), is connected with 

 the absence of active cones, it may be too early to discuss. 

 Some very lively springs on a large mudlump off Stake Island 

 on that Pass, in which the gas emitted is about equal m bulK 

 to the water, rise in small basins excavated at the foot o a 

 large cone which must have been 15 to 18 ft. high ; but tne 

 material they bring up is so very sandy that the water runs o 

 perfectly clear, f 



Mudlumps in the Marshes.— 1 have before remarked, that at 

 the present time, the upheaval of mudlumps on the passes, ana 

 subsequent silting up of the shallows between them (by n^^ 

 deposit, as well as by the degradation of the lumps theniseius^ 

 seems to be tlie normal mode of progression of the delta. ^^ 

 more advanced portions of the narrow bands of shore n^ 



