23 ON THE GEOLOGY OF LOWER LOUISIANA 



howevpr, they led to the conchision that the long-known outcrop at Port Hudson 

 was but the representative of a wide-spread formation, playing an important part 

 in the configuration of the Gulf coast region, and to which, in publications made 

 since, 1 have attached the name of its typical locality. 



More extensive observations for which I have had opportunity since then, while 

 extending greatly the scope of the group so designated, have also compelled a 

 modification of the definition given in the abstract, first published, of the results of 

 my first exploration.^ And as the data are nowhere given in their entirety, I shall 

 here recapitulate those not included in the preceding record. 



So far as my own observations extend, and so far as I have been able to gather 

 from those of others (especially from the valuable Report on the Mississippi River, 

 by Humphreys and Abbot), a blue clay stratum, usually containing stumps or trunks 

 of the cypress, or other lowland trees, extends not only over the entire alluvial 

 plain of the Mississippi, as high as Memphis at least; of Red River, as high as 

 Shrcveport, and correspondingly in other larger tributaries both of these rivers and 

 of the Gulf of Mexico ; but also over the entire coast region of Texas, Louisiana, 

 Mississippi, and Alabama, from the Rio Grande to the Escambia, and doubtless 

 farther, along the coast of Florida. It forms, along these coasts, the "blue clay 

 bottom" so well known to navigators, that generally, at a distance varying from 

 seven to twenty miles out from the mainland, breaks ofi" into deep water. 



I must here recall to mind my observations on the coast of Mississippi Sound, 

 made in 1859, and published in my report on the Geology of Mississippi, pp. 154 

 to 156. T found that while at a few points deposits apparently belonging to the 

 age of the Stratified Drift, extend to within a few miles of the coast, the greater 

 part of a littoral belt about twenty miles wide is underlaid by a solid, tenacious 

 blue or bluisli-black clay, which is everywhere struck in wells, crops out on the sea- 

 beach, and forms the "blue clay bottom" oft' the coast. C^ypress stumps, as well 

 as logs of various kinds, are constantly found in it; when penetrated, it is frequently 

 found to be miderlaid by sandy marine deposits, and at one point I found marine 

 shells in it. Higher up (at Saucier's, on Wolf River), I foimd a deposit precisely 

 similar to the stump stratum at Port Hudson, with cypress stumps and knees ; as 

 well as, not far off, a deposit containing twigs and burs of Bottom Pine (Phius 

 t(vda). Similar deposits are reported to occur frequently in the region. And the 

 same has been repeatedly asserted to be the case on INIobile Bay, by Hale and others. 



Port Hudson lies nearly due west of the locality above referred to. The level 

 tract of country in which it occurs, is bordered northward by a rather abrupt shore- 

 line of Drift hills." The same, according to Dr. Little's late observations, is the 

 case northward of Port Hudson ; while eastward of that place, a level or slightly 

 undulating plateau extends, with a gradual slope, towards Pearl (and Wolf) River. 

 This region has lately been explored by Dr. Hopkins,^ who fully confirms the identity 



' Amer. Journ. Scl., Jan. 18G9. 



= Miss. Eep. 1860, p. 385. 



' Second Annual Report of the Geol. Survey of Louisiana. 



