1896.] ^^^ [Smith. 



were found iu the uuderl^-iiig Carbouiferous. As lias been already men- 

 tioned, the ammonite genus Medlicottia is not a foreigner on this side of 

 the Permian Pacitic ocean, because its ancestor, Pronorites, is found 

 here too. 



The Triassic Pacific Ocean. 



Our knowledge of the Triassic Pacific ocean is based on the work of 

 Mojsisovics, ArktiscJie Triasfaunen.^ We find that in this period the 

 American part of the great western ocean has mostly become land, and 

 only on the westei'n border of ximerica do we find marine Triassic beds, 

 in Nevada, California, Idaho, and along the coast region in widely sep- 

 arated places, from Alaska through British xlmerica to Peru. 



Tliese deposits, with similar faunas, can be traced on the other side of 

 the Pacific from jSTew Zealand, Timor, New Caledonia, to Japan, and 

 Siberia. This sea stretched out on one side over the Himalayas to the 

 eastern Alps, forming what Neumayrf called the "central Mediter- 

 ranean sea." On the other side the sea stretched up to Spitzbergen, 

 but did not reach the Atlantic region. The Triassic was a continental 

 period for the greater part of the present continents.:}: After the Trias 

 the outlines of the western ocean had changed entirely, and no resem- 

 blance to the original boundaries can be traced. 



Time op the OcAriiiTA Uplift. 



The youngest rocks known to take part iu the Ouachita Mountain 

 system belong to the Upper Coal Measures, and the disturbance must 

 have taken place at the border l)etween Carboniferous and Permian. 

 Still, it is not unlikely that deposits of Permo-Carboniferous age may 

 yet be found at some places in the region. 



Another fact that makes this time for the uplift probable is that the 

 Permo-Carboniferous beds of Kansas and Nebraska are not of the open- 

 sea type, but belong to the northern European or Zechstein type of de- 

 posits. The beds of Texas, presumably of nearly the same age, are of 

 the Artinsk or open-sea facies, and are characterized hy the occurrence 

 of ammonites, commingled with ordinary Upper Coal Measure fossils. 



This uplift may be of the same age as that movement in the Appa- 

 lachiausg which cut off the Upper Barren Coal Measures of Pennsylva- 

 nia and West Virgiuia|i entirely from the western sea ; in those deposits 

 no marine fossils are found, but only land plants and fresh-water Crus- 

 taceans, T[ and a few fresh-water mollusks. 



* Mem. Acad. Imper. Sci. St. Petersbourg, Tome 33, No. 6. 



■\ Denkschrift Wiener Akad., 1885, ''Die geographische Verbreitung der Juraformation." 



I Suess, Antlitz der Erde, ii, p. 147. 



I Penna. Second Geol. Smvey, P. P., p. 120. 



II I. C. White, Bull, mh U. S. Geol. Survey, p 41. 



^ Penna. Second Geol. Survey, P. P., Permian Flora, \V. M. Fontaiue and I. C. White, p. 

 116. 



PROC. AMEK. PHILOS. SOC. XXXV. 152. 2 D. PRINTED DEC. 3, 1890. 



