EEPORT OF THE SECRETARY. 37 



answered by further investigation. The following is an abstract of 

 the results already obtained : 



" The Port Hudson deposit described by Carpenter, Lyell, and others, 

 is the cypress swamp equivalent of the ' bluff formation,' just as the 

 existing cypress swamps correspond to the Mississippi alluvium. The 

 three islands, (out of the chain of five,) which were examined, con- 

 sist of outliers of 'orange sand, 7 which has resisted denudation; 

 on and around which, strata precisely similar to those of Port Hud- 

 son have subsequently been deposited. The rock-salt of Petite 

 Anse island underlies the orange sand, and is, therefore, anterior to 

 the drift, and it may probably be reached at points much higher 

 above tide level than has been supposed, obviating the chief diffi- 

 culty (that of drainage) heretofore experienced in working the 

 deposit, the lowest part of which only has thus far been explored. 

 While the precise position of the deposit, as regards the inferior 

 formations, cannot now be determined, the results of the boring of the 

 New Orleans artesian well render the conclusion almost unavoidable, 

 in view of the absence of all signs of disturbance on the coast, that 

 the salt deposit is of an age corresponding to that of the strata pen- 

 etrated in this boring, which there is reason to believe are post-ter- 

 tiar}'. Apart from all these comparatively ancient deposits, the entire 

 delta is underlaid at or near tide levels by a cypress swamp deposit, 

 as it would seem, of later date ; and beneath these, as well as the 

 more ancient deposits of a similar nature, there are beds of gravel of 

 a, composition similar to that of the main or Mississippi branch of the 

 great stream of the orange sand epoch, which here appears to have 

 divided into two branches, one reaching the gulf in the region of 

 Vermillion bay, the other on or near the Sabine. Important 

 information was obtained concerning the formations of northern Lou- 

 isiana, which, while of course corresponding in general to those of 

 Mississippi, differ so far as to promise a ready determination of 

 the age of the grand gulf groups, which thus far remains in doubt, 

 notwithstanding that those groups cover nearly half of the State of 

 Mississippi, filling the space between the eocene and postpleiocene 

 deposits. All that is known of it, is, that during its formation, palms 

 flourished on the borders of an immense lake or everglade, which 

 either bordered, or itself represented, the present gulf of Mexico. 

 After what has been observed in Louisiana, there is less difficulty 

 in accounting foi the total absence of animal fossils from this forma- 

 tion in Mississippi." But the problem to be solved regarding its age, 

 extent, and relations to the eocene and quaternary shores of the gulf 

 is one of so much interest that while in Louisiana Mr. Hilgard was 



