16 ON THE GEOLOGY OF LOWER LOUISIANA 



The last six feet were penetrated with the auger. So much water flowed in 

 (tlirough the gravel apparently) that it became necessary to exclude it if possible. 

 This was attempted by cementing the curbing to the salt with pitch ; but the 

 presence of the water prevented a thorough adhesion being attained, and thus the 

 shaft, at the time of my visit, was "drowned." 



The surface of the salt where struck was estimated to be perhaps as much as 

 seven feet above tide-level ; higher than at any point previously reached. 



The semi-indurate sandy material, No. 4 of the section, is the same as that which 

 crops out in several neighboring ravines, and is precisely similar to the material of 

 the Drift at Weeks' Island. The under-lying pebble-bed, with subjacent bluish 

 pipe-clay, is likewise characteristic of the same formation. 



There can, therefore, be no reasonable doubt tliat the salt deposit underlies, and 

 is older than, the Orange Sand or Stratified Drift Formation. 



It is true that the identification of this formation here, as wcU as at AVecks' 

 Island, rests merely upon stratigraphical and lithologii-al characters. But these, in 

 the case of these deposits, are so well defined and characteristic everywhere, that 

 even the coincidence of fossils could add but little weight to the evidence. Silicified 

 wood, nevertheless, the almost constant concomitant of the formation, is quite 

 common on the island, and the pebbles speak of high northern origin. 



It must be remembered, too, that we are here dealing, not with a wide range of 

 possible formations, but with small and partly local sub-groups of a comparatively 

 short epoch, which are well known to be characterized by differences of origin, 

 mode of deposition, and material, rather than by a diversity of living forms; save 

 such as may result from their special and local character. None of the deposits 

 likely to occur in the locality before us could be expected to contain other than 

 living forms in a fossilized state. The consistent ahsence of any such forms is one 

 of the distinctive features of the Orange Sand group. Another, is its stratification ; 

 a third, its current-worn, peroxidized, non-calcareous materials; excepting alone the 

 case of angular fragments of silicified wood, which evidently came down originally 

 as drift-wood, and has subsequently suft'ered silicification in situ. (Miss. E.ep., 1860, 

 p. 20 and ff.) 



Lastly, the pebble-stratum everywhere found overlying the salt, and also occurring 

 at higher levels, establishes some important points in the identification. The 

 average size is from that of a large hen's egg to that of a guinea-fowl's; some of 

 the quartz-pebbles, however, weighing a poimd and over. Some of the latter, as 

 well as some large sandstone pebbles, appear to be derived from the Grand Gulf 

 rocks, distant about sixty miles to the northward. The majority, however, consist 

 of brown or yellowish hornstone with impressions of palaeozoic fossils — crinoids, 

 corals, etc., of both silurian and carboniferous types. Jasper, agate, carnelian; also 

 graphic granite, syenite, mica schist, and siliceous schist, are not uncommon. The 

 latter rocks, evidently of high northern origin, are almost unknown in the south- 

 western Drift, outside of the main pebble-belt of the Mississippi Valley. 



Dr. Goessmann mentions the occurrence of a large boulder of porphyritic diorite. 

 I have in vain sought, among the pebble-beds, for another sample of this rock, 

 whose home seems to have been Missouri or Arkansas. As it was found in the 



