E. W. Hilgard— Geology of the Delia, 



[Read before the American Association at its last meeting in Troy.] 

 In previous papers* read before this Association, I have com- 

 municated the results obtained during two successive geological 

 expeditions to Louisiana, so far as the more ancient formations 

 are concerned. It is the object of the present communication 

 to present and discuss the phenomena of that portion of the 

 territory explored by me, lying within what is usually con- 

 sidered the alluvial area proper, or Delta, of the Mississippi 

 river. Most of these observations were made in 1867, during 

 the first of these excursions referred to, under the auspices of 

 the Smithsonian Institution; their publication having been 

 delayed in consequence of want of time, on my part, to carry 

 out the large amount of chemical and microscopic work in- 

 volved in the discussion, which is even yet far from being as 

 full as would be desirable. I hope, however, to be enabled. 

 hereafter, to continue the investigation of the subject, both in 

 the field and in the laboratory.f 



I. The Upper Delta Plain. 

 I recall to mind the fact that, as we descend the Mississippi. 

 the older strata successively sink from view. A few miles 

 below Vicksburg we lose sight of the older Tertiary. Thence 

 down to the latitude of Tunica Bend, La., we find the rocks ot 

 the Grand Gulf (Tertiary) age, possessing but a very famt soutn- 

 ward dip. Next, the oldest representative of the Quaternary 

 epoch, viz., the stratified Drift or Orange Sand, disappea^ 

 beneath the water's edge near Port; Hudson ; while the swamp, 

 lagoon and fluviatile beds, which have given ii^toriety to ^ _ 

 latter localitv, are seen above high water level not much tartner 

 south than the city of Baton Eouge. „ , g 



The gradual descent and successive disappearance ^i.^^^^^ 

 strata is not, however, altogether a phenomenon of dip, i 

 • This Joura:.l, II, vol. ilvii. Jan. 1869 ; Ibid., xlviii, Not. 1869. ^^ 



t Fof material assistance in the investigations embraced m ™ » pap^ • g^^. 

 especially indebted to the officers of the Delta Survey in charge of the ^^ ^^ 

 vey schooner Varina— Messrs. F. P. Webber and Henry L. Mannden, wr t^^^ 

 of observations and specimens furnished ; to Capt. Day, in commana oi ^^ 

 Tes-el, then moored at the Head of the Pi.sses, for a boat's crew fr^^^^ell 

 assistance in the examination of the mudlumps; to Mr. Moultop of thej 



indebtedto D? Co^el, p'esw'ent of _th^ N^. ^^Aca^^ 



I, as well a« other men-bers of that body. Other 

 1 m their proper places. 



