NATURAL SCIENCES OP PHILADELPHIA. 138 



over the far south-west. This conclusion is also borne out by the statements 

 of Capt. Marcy and other explorers of that region. The facts given by this 

 gentleman and Dr. G. G. Shumard, likewise point to the conclusion that the 

 great gypsum deposits of the south-west hold a position equivalent to No. 2, or 

 the upper part of No. 1 of the Nebraska section. 



From all the facts, we are led to believe, as stated on a former occasion, that 

 the divisions No. 4 and 5 of Nebraska, and their equivalents in New Jersej' and 

 Alabama, are entirely wanting, or but meagrely represented, throughout the 

 south-west; and that No. 2 and No. 3 are the main fossil-bearing strata of that 

 region ; while No. 1, which there as in the north-west and in Alabama, rei)0ses 

 on Carboniferous strata, attains a much greater development than in either of 

 those countries. 



Conclusions. 



Ist. We have no evidence that any of the Tertiary deposits now known in 

 Nebi-aska are older than Miocene. 



2d. The estuary and fresh-water deposits at the mouth of Judith River are 

 probably on a parallel with the lowest bed of the Great Lignite basin, though 

 some portions of them ~iay be so.mewhat older. 



'dd. The Great Lignite basin and the Mauvaiies Terres of White River, though 

 probably both Miocene, are not exactly on a parallel. 



Ath. We have in Nebraska a more complete series of Cretaceous formations, 

 and consequently a better standard of comparison for rocks of that age, than is 

 yet known to exist in any other portion of this country. 



bth. The formations in New Jersey and Alabama generally referred to the 

 Cretaceous system, are on a parallel with the iqjper and lower members of the 

 Nebraska section, (No. 1, 4 and 5 ;) while nearly, if not quite all the main fossil- 

 bearing deposits older than Tertiary, and newer than Carboniferous, in Kansas, 

 Arkansas, Texas and New Mexico, are on a parallel with the middle and lower 

 portions of the same. 



Qlh. Although the beds No. 2 and 3 of the north-west, are extensively de- 

 veloped, and probably the principal fossiliferous Cretaceous deposits of the far 

 south-west, we have up to this time, no evidence of their existence east of the 

 Mississippi. Consequently the marked typical differences observable between 

 most of the Cretaceous fossils hitherto found in the south-west, and those 

 characterizing the upper Cretaceous formations of Nebraska, Alabama and 

 New Jersey, are not wholly due to the fact that they belonged to different zo- 

 ological districts ; nor yet, as might be supposed in regard to the Nebraska and 

 New Jersey species, to the modifying effects of physical conditions dependent 

 on latitude ; but mainly to the fact that they belong to another geological hori- 

 zon, and consequently lived during a different epoch. 



7th. There is at the base of the Cretaceous System, at distantly separated 

 localities in Nebraska, Kansas, Arkansas, Texas, New Mexico, Alabama and 

 New Jersey, if not indeed everywhere in North America where that Sys- 

 tem is well developed (at any rate east of the Rocky Mountains), a series of 

 various colored clays and sandstones, and beds of sand, often of great thickness, 

 in which organic remains, excepting leaves of apparently dicotyledonous plants, 

 fossil wood, and obscure casts of shells, are very rarely found, but which every- 

 where preserves a uniformity of lithological and other characters, pointing 

 unmistakeably to a similarity of physical conditions daring their deposition, 

 over immense areas. 



8th. Although the weight of evidence thus far favors the conclusion that this 

 lower series is of the age of the lower Green Sand, or Neocomien, of the old 

 world, we yet want positive evidence that portions of it may not be older than 

 any part of the Cretaceous System. 



1857.] 



10 



