30 ON THE GEOLOGY OF LOWER LOUISIANA 



gestion, I now feci satisfied that the maximum of solar heat available at one and 

 the same time would have been utterly inadequate to produce such masses of water 

 as have manifestly been active in the formation of the Southern Drift. More- 

 over, if it be true, as Western geologists assert, that the main body of the Drift of 

 the Northwest is the result of iceberg transpcti-tation, while the deposits are 

 altogether destitute of contemporary marine fossils : the conclusion is inevitable 

 that the icebergs floated in a vast inland glacier-lake. 



What might have been the northern shores of this fresh-water Mediterranean 

 under the circumstances then existing, I must leave to those better acquainted 

 tlian I am with the topographical features of that region, to discuss. Possibly the 

 glaciers themselves may have formed a sufficient barrier. Towards the east, south- 

 east and southwest, it woiUd have been defined by the Alleghany, Cumberland, and 

 Ozark ranges, its main outlet lying, doubtless, in the axis of the Mississippi Valley, 

 the gap between the Ozark and Cumberland highlands, not having as yet been 

 eroded to its present level. Any somewhat sudden break in this lowest portion of 

 the barrier, such as is apt to occur even where erosion is the only agent (leaving 

 out of consideration the very possible agency of earthquakes precisely in the critical 

 region about New Madrid) would then produce precisely the phenomena we now 

 observe at the South, viz., the action, at first, of violent currents plowing up and re- 

 depo.iiting the material of the more ancient formations ; carrying down in the main 

 channel rocks of high northern derivation, far out into the Gulf; I'e-stratifyiug or 

 " modifying," towards the end, a good portion of the iceberg drift of the Northwest, 

 in loco ; and simultaneously, as the velocity of the currents diminished (either from 

 exhaustion of the reservoir or incipient depression), coA'ering over the pebble-streams 

 and eroded surface of the South, Avith the peculiar "Orange Sand," which cliarac- 

 terizes the delta-shaped mass covering the States of Mississippi and Louisiana, as 

 well as part of the adjoining ones of Tennessee, Alabama, Arkansas, and Texas. 



One of the characteristic features of this "Orange Sand" (a name it might be 

 desirable to retain as descriptive of a peculiar facies of the southern Stratified Drift) 

 ifc the complete peroxidation and lixiviatiion of its materials.' Protoxides of iron 

 and manganese, as well as lime, magnesia, and alkalies, are reduced to their mini- 

 mum in this most barren formation. All this argues, so far as it goes, long subaerial 

 exposure, such as has manifestly not acted upon the Northwestern Drift; and this 

 agi»in confirms the argument upon purely geological grounds, tending to prove the 

 elevation of the southern slope above the sea-level, even subsequent to the Drift 

 epoch proper. 



if the hypothesis here advanced be deemed too bold, or premature, I submit that 

 at least it subsumes among its possibilities all the phenomena now known concerning 

 the Drift of the interior and Gulf States; and in this point of view may serve at 

 least as a definite basis for investigation, until a better one be found. So far as I 

 am aware, there is nothing in the geological structure of the region between the 

 Cumberland and Ozark highlands, to compel the assumption that its degradation is 

 not of comparatively modern date. The rocky channel of the Mississippi, from St. 



• Miss. Rep., 18G0, pp. 15, 23, 21. 



