2y ON THE GEOLOGY OF E W E R L O F I S I A N A 



of outliers protruding through the Tertiary, tliat truAcrses Louisiana, from its 

 northwest corner, in the direction of Vermilion Bay. 



'2d, The remarkable gap in the tertiary series, the entire interval between tlie 

 Eocene and Drift periods being represented only by the almost non-fossiliferous 

 brackish or fresh-water beds of the "Grand Gulf" rocks; showing that during that 

 time, the Gulf of Mexico was not a marine basin, but probably cut off from com- 

 munication with the Atlantic by an upheaval in the Antilles, or Caribbean sea. 



3d. The continuity of the "stratified" or "modified" Drift of the Northern 

 States, with the great stratified Drift or "Orange Sand" formation of the South, 

 now identified from Baltimore, Maryland, around the Appalachian upheaval to the 

 Colorado of Texas. 



As regards the first mentioned point, its influence upon succeeding formations 

 has been, as regards the early Tertiary, the replacement, to a large extent, of the 

 marine strata observed in Alabama and Mississippi, by lignitic fresh or brackish- 

 water equivalents in northern Louisiana. Red River valley evidently marks a deep 

 gap in that ridge, wherein the Grand Gulf rocks have been deposited without any 

 notable variation of character. A short distance southward from Red River, how- 

 ever, we find the cretaceous outlier near Chicotville; and following the general 

 trend of the outcrops, we meet, on Vermilion Bay, the remarkable elevations of the 

 Five Islands, whose geological structure I have above discussed. The Drift which 

 in the Calcasieu bores is struck at a depth from one hundred and sixty to three 

 hundred and fifty feet below the sca-lcvel, and disappears beneath the Port Hudson 

 series at Proffit's Island near Port Hudson, and above Chicotville, is here found at 

 and above the Gulf level; while again at New Orleans, in the axis of the Mississippi 

 embaymcnt, no Drift has been reached at six Inmdred and thirty feet. 



It is scarcely credible that while heavy pebbles were carried from beyond Cairo 

 to the shores of Vermilion Bay, no corresponding deposits should have been made 

 in nearly the same latitude, in the axis of the valley; imless, indeed, deep water 

 checked the transporting power of the current. But if deep water prevailed at 

 New Orleans at the time of the Drift, then of course the deposits that have since 

 filled up the trough are posterior to the Drift — in other words, are the equivalents 

 of the Port Hudson series, which elsewhere along the coast is found overlying the 

 drift, and could not very well be unrepresented in the deepest part of the valley. 

 Only we should expect the character of the deposit here to be very predominantly 

 marine (not altogether, since it was the main outlet of the continental waters); and 

 so I have found it to be, in my examination of the specimens from the New Orleans 

 artesian wcU.^ 



It is stratigraphically almost impossible that the strata penetrated here should be 

 of an age anterior to the Drift, i. e. pleiocene; a few unknown (or possibly extinct) 

 species occurring in them to the contrary notwithstanding. AVhcther or not the 

 drift be actually underlying these marine strata, will, I hope be settled before long, 

 in the interest of the water-supply of the city of New Orleans. But if in Calcasieu, 



' Rep. U S. Engineer Dcp't for 1870. 



