PERMIAN PERIOD. 371 



Streptorhynchus Umbraculum (fig. 550). Chonetes Flemingii N. & P. 



" Missouriensis Swallow. Rhynehonella Osagensis, Swall. 



Spirifer cameratus (fig. 591). Athyris subtilita Hall. 



*' planoconvexus Shumard (=S. Urii ?) Mytilus rectus Shumard. 



" pectiniferus ? Sow. Myalina subquadrata Shumard. 

 Productus semireticulatus (fig. 229) Martin, " Kansasensis Shumard. 



" Rogersi (fig. 592) N. & P. Allorisma Minnehaha Swall. 



" aequicostatus Shumard. Naticopsis Prieei Shumard. 



The species Monotis Haiti Swallow, and two or three others, occur in both 

 his Upper and Lower Permian. M. Hawni M. & H., M. concava, Bakewellia 

 antiqua, Solen (?) Permianus, Schizodus Rossicus, Murchisonia mbangulata ?, 

 Nautilus Permianus, Orthoceras Kickapooense, Cyrtoceras dorsaium, are found 

 only in the Upper. 



HI. General Observations. 



The several points west of the Mississippi at which the Permian 

 rocks have been found, prove at least their wide distribution over 

 the Rocky Mountain slopes, although now to a great extent covered 

 by strata of later date, — the Triassic, Jurassic, Cretaceous, and Ter- 

 tiary. We observe the following facts connected with the period : (1.) 

 The beds are apparently all marine strata, for the fossils are marine. 

 (2.) The numerous alternations between impure limestones and clays 

 and some sand deposits indicate oscillations through the period in the 

 depth of water between moderate depths and very shallow waters. 

 (3.) The absence of coal beds is proof of no fresh-water Carboni- 

 ferous marshes in the regions where the rocks have thus far been 

 examined, (4.) The non-occurrence of these marine strata over the 

 region east of the Mississippi (with perhaps a single exception near 

 the river in Illinois) seems to show that this eastern part of the 

 continent was dry land. Early in the Carboniferous period, the 

 Pennsylvania region was raised and became dry even of its old 

 marshes, for only the Lower Coal measures occur there ; and in the 

 Permian period, as it appears, the dry region had extended so as 

 to include all the country east of the Mississippi. (5.) The beds 

 occur within the same region, or on the borders of the same region, 

 in which the Coal formation during the Carboniferous period was 

 represented by limestones ; that is, in the great interior sea which 

 had so long existed as the Palaeozoic representative of the Gulf of 

 Mexico, — a comparatively shallow, but extensive, inland sea stretch- 

 ing northward. The present western limit of the Gulf is nearly in 

 a north-and-south line with the western boundary of the State of 

 Kansas. 



The existence of these Permian deposits is, then, owing to a con- 



