THE QUATERNARY FORMATIONS. 



326. The quaternary, or post-tertiary formations of Mississippi, 

 seem to subdivide very naturally into five successive stages or 

 periods, viz: Lowest, immediately overlying the latest Tertiary, 

 the Orange Sand formation, corresponding, probably, to the drift of 

 the Northern States. Next above, the Blvff formation of the Mis- 

 sissippi River ; a calcareous silt deposit containing, in Mississippi, 

 chiefly or only terrestrial fossils. Succeeding this, we find the 

 Yellow Loam deposits, which form the basis, as it were, of the agri- 

 cultural wealth of the upland portion of the State. Still more 

 modern are the Second Bottom or Hommock deposits, which, while 

 they show a very obvious relation to the water-courses as at pres- 

 ent existing, still must have required a state of things different 

 from the present, to produce them ; and latest of all are the Allu- 

 vial deposits, whose formation is referable to causes still in action, 

 including all the soils, first-bottom deposits, sand drifts, etc., now 

 in pi ogress of formation. 



I. THE ORANGE SAND FORMATION 



Has been treated of at the beginning of this volume, out of its 

 proper geological order, for reasons there explained (Tl5, ff.) 



II. THE BLUFF FORMATION. 



327. The deposits of this formation, whose characters seem fo be 

 identical, in almost all respects, with those of the beds so named 

 by Prof. Swallow, in Missouri, occupy a narrow belt, along the 

 borders of the Mississippi Bottom in N. Mississippi, and along the 

 river itself in the southern portion of the State. In the whole of 

 this territory, so far as I am aware, it exhibits a lemarkable uni- 

 formity of character ; consisting of a fine silt, almost too siliceous 

 to be called a loam, of a grayish or yellowish buff tint ; which effer- 

 vesces throughout its mass in consequence of a certain percentage 

 of the carbonates of lime and magnesia, and contains, besides, 

 irregularly shaped, often tubular, concretions, from the size of sand- 

 grains to the weight of several pounds, consisting of the carbonates 

 just mentioned, with some of the silt intermixed. The whole mass 

 is lightly cemented by these salts, so far as to impart to it a cer- 

 tain degree of firmness, which it loses when once broken tip. Al- 

 tlu ugh profiles of as much as seventy ieet are sometimes seen, 

 consisting altogether of this material, itis in most cases extremely 

 difficult to find any definite marks of stratification, which I have 



