EVIDENCES OF OSCILLATIONS OF LAND AND SEA. 333 



of this formation has been erroneously used in connection with them in 

 a recent j^ublication.* 



Paleontologically these beds of the western shorehne show slight 

 variation from those of the east. The same distinguishing species, such 

 as Gryphsea mucronata, Gabb, 0. quadricosiata, Shumard, Trigonia emoryi, 

 Conrad, of the Denison beds, and Schloenbachia leonensis of the Fort 

 Worth, occur, but some new species, such as Grgphsea dilatata, Marcou, 

 and Tarhinolia texana, Conrad, are initiated, and some of the Comanche 

 Peak species, such as Chemmizla occldentale, Gabb, range up into the 

 A\\ishita. These variations over such ^reat distances are naturall}^ to be 

 expected, and their stud}^ will ultimately enable us to correlate all syn- 

 chronous deposits of Washita time over the Mexican and South American 

 region. 



Each of the littoral formations shoring against the Ouachita mountain 

 system should be studied in its extent and variation over the archi- 

 benthal region southward and the results set forth in the same way as I 

 have endeavored to present my studies of the Washita division. 



Oscillations of Land and Sea recorded in the Region. 



Wliere sediments present such a uniform and persistent extent as the 

 members of the section of this region, and where they are found in such 

 definite succession, it is possible to make some very accurate interpreta- 

 tions from them of the subsidence and elevation of that portion of the 

 ocean's margin in which they were laid down and of the land from which 

 they were derived. The stretch of Plateau gravel across Arkansas and 

 Texas for 600 miles at the elevation of 500 to 600 feet can mean nothing 

 else than that they once marked a marine level of deposition, and that the 

 land has been elevated to the present height since they were laid down. 

 Furthermore, this elevation was not local or spasmodic, but general or 

 epirogenic. In this region we have records since early Mesozoic time of 

 five of these periods, when the oscillations of the land and sea have 

 brought the region to marine level or elevated it far above. The records, 

 so far as they can be interpreted, are as follows : 



The earliest, where our studies begin, is the Trinity shoreline, which 

 marked the great baseleveling of the land and its invasion from the 

 southward in late Mesozoic time by the waters of the Atlantic. They 

 are, at their beginning, littoral near-shore deposits, as shown by their 

 structure and organic remains. 



The Glen Rose beds, mostly l)recciated and chalky limestones and 



* See American Geologist, November, 1893, pp. 309-314. The paleontologic nomenclature, range 

 and formation names used in tliis article are unreliable. 



