December 28, 1906.] 



SCIENCE. 



865 



proper^ deposited in the marshes above during 

 the twiee-annually recurring floods of the 

 great river. 



Among the details of the investigation, 

 given in my article above referred to, the 

 following are of interest as corroborative of 

 the above explanation of mudlump phenomena. 

 The microscopic character of the ejected mud 

 is precisely that of the mud brought up by 

 the sounding-lead from the seaward slope of 

 the river bar. There is a mixture of fresh- 

 water organisms and debris with marine 

 forms such as f oraminif era ; but these in the 

 mudlump ejecta are in a macerated condition. 

 The water accompanying the outflowing mud, 

 or sometimes welling up clear from old or 

 sandy vents, shows the chemical nature of 

 diluted sea-water subjected to maceration with 

 decaying organic matter. That is to say, its 

 sulphates have been reduced to iron pyrites, 

 which is scattered in shining crystals through 

 the mud, while the water is strongly impreg- 

 nated with bicarbonates of lime, magnesia and 

 iron, so that it turns turbid on exposure to the 

 air. Taking the common salt as the basis 

 of comparison, the proportion of magnesium 

 chlorid is increased, that of potash decreased; 

 the latter doubtless by the absoi-ption of the 

 base into zeolithic combination. 



The gas from a vent on the Passe a I'Outre 

 consisted of 86.20 per cent, of marsh gas, 9.41 

 of carbonic dioxid, and 4.39 of nitrogen. This 

 approximates closely to the average composi- 

 tion of the gas from ordinary swamps. No 

 oxygen was present. 



The commercial importance of the forma- 

 tion of mudlumps is well illustrated in the 

 history of the several outlets or passes during 

 historic times. The earliest navigation from 

 the gulf to New Orleans was almost wholly 

 through the * Passe a I'Outre,' the most north- 

 erly of the mouths, whose very name indicates 

 its chief importance as the outlet for deep- 

 sea vessels destined for ' outre-mer ' ; with the 

 northeast pass, it remained the main outlet in 

 use even to the first third of the past century. 

 Then it became so contracted and shallowed 

 by mudlumps that the northeast and southeast 

 passes were for a while the main channels 

 used by vessels; but these also being soon 



heavily obstructed by lumps, and the south 

 pass being too narrow and shallow for deep- 

 sea ships, the southwest pass was, during the 

 greater part of the past century, the main 

 outlet for navigation. Its channel being very 

 wide and its deposits more sandy by reason 

 of its being most nearly in line with the main 

 river at the head of the passes, its use in- 

 volved the additional difficulty of shifting 

 sand bars. To keep a navigable channel 

 through these and the copious mudlump for- 

 mations was an endless task, and cost the gov- 

 ernment millions; besides necessitating the 

 use of enormously powerful tugs for the ship- 

 ping. After many unsuccessful attempts for 

 permanent relief, all of which were frustrated 

 by the rise of mudlumps, came Eads's proposi- 

 tion to turn the river into the south pass, the 

 mouth of which was then free from mud- 

 lum-ps. While this matter was before con- 

 gress, the writer called Eads's attention to the 

 almost certainty that whenever the south pass 

 should be made the main outlet, mudlump 

 upheaval would surely occur. Eads replied 

 that he hoped that the increased velocity of 

 the current in the narrow channel inclosed by 

 his jetties would keep it scoured out to a much 

 greater extent than the shallow southwest 

 pass had been, and that at any rate it should 

 be tried as an ultima ratio, and allowed to 

 go unchallenged. To this, of course, I agreed. 



The event has in the end justified both 

 Eads's and my anticipation. Not many years 

 after the completion of the jetties and wing- 

 dams, mudlump upheaval began inside of the 

 south pass bar; but the watchful activity of 

 dredgers, together with the scouring action of 

 the full river current, are successfully keep- 

 ing the channel in navigable condition, at 

 very much less current expense, and much 

 more effectually, than could ever be accom- 

 plished in the southwest pass. 



Taken altogether, these unique phenomena 

 characterizing the formation and progression 

 of the Mississippi delta seem to be of sufficient 

 importance, both theoretical and practical, to 

 render their omission from handbooks of 

 American geology and hydrology hardly ex- 

 cusable. It is expected of those who write 

 such treatises that they should acquaint them- 



