Area in Louisiana and Eastern Texas. 85 



but it has since been uncovered by erosion ; farther east it is still 

 concealed. 



VIII. The Carboniferous beds uncovered in Texas all belong 

 to the Upper Coal Measures ; it is inferred that a greater thick- 

 ness is still covered. 



IX. The character of both the Silurian [Cambrian, Ordovi- 

 cian, Silurian, and Devonian] and Lower Coal Measures [Mis- 

 sissippian and Pennsylvanian] sediments of the Ouachita uplift 

 show that they came from the south, so that the land area must 

 have been in that direction during Paleozoic times. 



X. The sea occasionally invaded both the Arkansas and Texas 

 synclinal troughs during Coal Measures times, but coal-forming 

 conditions obtained in the Texas syncline later than in the Ar- 

 kansas basin. 



XI. The Tertiary depression was probably more marked on 

 the Arkansas than on the Tennessee side of the embayment ; this 

 is shown by the Cretaceous border being concealed by the Ter- 

 tiary deposits in Arkansas, while in Tennessee, Mississippi and 

 Alabama they are exposed in a broad belt." 



Arthur Winslow, who studied the Carboniferous rocks 

 in the Arkansas Valley in Arkansas about 30 years ago, 

 expressed the opinion that ^^the similarity between the 

 structure of this area and that of the Carboniferous area 

 in Pennsylvania is not a mere accident, but is due to a 

 trans-Mississippian extension of the same cause. "^^ He 

 thus appears to to have believed in the extension of the 

 Appalachian land area across the lower Mississippi 

 Valley. 



The opinion that the Appalachians extended westward 

 across the lower Mississippi Valley into Texas has also 

 been expressed by other geologists, though they have held 

 that there were times when the lower part of this valley 

 was submerged, so that the Paleozoic land area to the 

 west was disconnected during such times from the main 

 part of the Appalachian land area to the east. The 

 opinions of different paleogeographers on this matter as 

 they are expressed on their maps are given below for the 

 Paleozoic era, and for the Triassic and Jurassic periods. 



Stuart Weller,^^ who published two paleogeographic 

 maps in 1898, held that the southern end of the Appala- 

 chian land area extended westward across the lower 



°^ Winslow, Arthur, The geotectonic and physiographic geology of western 

 Arkansas, Geol. Soc. America, Bull., vol. 2, p. 231, 1890. 



*" Weller, Stuart, Classification of the Mississippian series. Jour. Geology, 

 vol. 6, pp. 306-308, 1898. 



