100 



sippi," that "niudlunip formation is at present tlie normal mode of pro- 

 gression of the visible delta into the gulf, the principal mudlumps rising 

 immediately inside the bar, where the current excavates the river bed so 

 as to relieve the superincumbent pressure." As to tlie origin of these mud- 

 lumps. Prof. Hilgard further states in substance (loc. cit.) that "in the 

 Mississippi delta region there is an impervious blue clay bottom reaching 

 out into the gulf for about twenty-eight miles beyond the present mouths 

 of the river," that "superimposed on this is a semi-fluid blue clay stratum," 

 and that "over this in the swamp-delta areas are deix)Sited sandy bar 

 material much faster than the former can escape to seaward under pres- 

 sure. Consequently, wherever the river removes the superincumbent sandy, 

 gravelly deposits, the pressure on the areas adjacent forces the semi-fluid 

 clay to the surface in the form of mudlumps. Escaping gases also seem 

 to aid in this mudlump formation." 



Now the mounds of the lower Mississippi-Texas region are not likely 

 identical with those of the delta proper in formation ; lint may they not 

 have been made in a similar manner; that is, on the principle of "creeps"? 

 If on an impervious bottom at the time the region in question was being 

 formed, there was a semi-fluid layer reaching any distance inland, as the 

 shore line advanced or receded, and this was being covered with another 

 layer faster than it could creep seaward, whether the superficial layer 

 was brought tliereby wind or water, mudlumps would certainly have been 

 pushed up in all the sjwts where the latter layer was thin or wanting. 

 'I'lu'se, when dried, would become mounds. 



