108 [October, 1841. 



isiana. I have elsewhere (Synop. p. 24,) considered them as indi- 

 cations of cretaceous deposits ; and my recollection induces me to 

 believe that their characters correspond either to A. Abyssinus or 

 A. borealis. 



Besides the preceding fossils from upper Missouri, Mr. Ni- 

 collet obtained the following species from the same interesting 

 locality. 



Ammonites Conradi (nobis,) Synop. PI. xvi. fig. 1, 2, 3. Large and 

 beautifully preserved specimens. 



Ammonites placenta, (Dekay,) Synop. pi. 2, fig 1. This species 

 is found from comparatively small dimensions to a gigantic size, 

 probably not less than two or three feet in diameter. 



Inoceramus Barabine (nobis,) Synop. PI. xvii. fig. 3, and PI. xiii. 

 fig. 11. This shell has hitherto been found only in Greene county, 

 Alabama, but appears to be abundant in the Mandan country, 

 often compressed and broken, but readily identified. 

 Baculites compressus, (Say,) Synop. PI. ix., fig. 1. This species 

 so nearly resembles B. ovatus of the same naturalist, from the 

 marls of New Jersey, that I am almost disposed to consider them 

 identical. The species in question is found of gigantic dimen- 

 sions, for example, more than a foot in length, and three or four 

 inches in diameter. 

 Belemnites Americanus, (nobis,) Synop. PI. 1, fig. 1, 2, 3. 



Hence it appears that among the small number of species no- 

 ticed on this occasion, at least four are found in deposits of the same 

 age on this side of the Mississippi, thus identifying the cretaceous 

 strata over an immense geographical area, which commences in 

 New Jersey, and perhaps at Martha's Vineyard, is traced in all the 

 Atlantic States to Georgia, thence through Alabama and Mississippi, 

 across the Mississippi to Louisiana, and Arkansas, where it is seen 

 on the plains of the Kiamesha. From this point until we approach 

 the Great Bend of the Missouri river, in the Mandan country, it has 

 not yet been traced; but in the last named region, about 1500 miles 

 above the mouth of the Missouri, it becomes again conspicuous as 



