DEVELOPMENT OF THE ACADIAN GEOSYCLINE , 181 



As we have seen, the Northumberland basin came into being with the 

 late Devonian orogen}', which was followed by fresh-water deposition of 

 early Mississippian time (Horton, 2,000 feet) and by late Mississippian 

 marine deposits (Cheverie, 700 feet, and AYindsor, 1,200 feet). Then 

 the ]^orthnmberland basin underwent momitain-making for the second 

 time, and, so far as known, this movement completely shut out marine 

 transgressions until the origin of the present Gulf of Saint Lawrence. 

 Following this second elevation, more than 5,000 feet of coarse conti- 

 nental deposits of early Pennsylvanian time were laid down in valleys 

 between mountains. Then came the third reelevation of the mountains, 

 followed by 6,800 feet of coarse sediments, also having many coal strata 

 whose floras indicate Middle Pennsylvanian time. Finally came the 

 fourth uplift, giving rise to from 2,100 to 6,000 feet of more or less red 

 beds of latest Pennsylvanian time, and then the whole of the Northum- 

 berland basin was reelevated in the early Permian for the fifth time. 



In all of this we see that the Acadian region was intensely folded and 

 intruded by igneous rocks during the late Devonian orogeny, and that it 

 Ihen underwent four widely spread times of seemingly vertical uplift, 

 with a final elevation in the Permian. Even so, these are not all of the 

 times this region underwent one or the other kind of crustal movement, 

 since the early Paleozoic formations of the Acadian geosyncline show in 

 the nature of their coarse sediments that the borderland Novascotica had 

 been uplifted in late and early Silurian times, probably also in the Ordo- 

 vician, and at the close of the Middle Cambrian. 



Development of the Ouachita Embayment 



(See Maps, Figures 5 to 11) 



One of the interesting phenomena in the stratigraphy of North Amer- 

 ica is the appearance in Upper Cambrian time of what seems to be the 

 beginning of a geosyncline all along the north side of the Mexican old 

 land known as Columbia and its northeastern extension, Llanoria. It 

 was a seaway that united the Cordilleran trough with the Appalachian 

 one, but it lasted only into Middle Ordovician time. 



Beginning in eastern Arkansas, the Cambro-Ordovician deposits of 

 this trough are seen emerging from underneath the Mississippi embay- 

 ment of Mesozoic and Cenozoic formations. They have a maximum 

 thickness of about 1,500 feet, increasing westward to 7,000 feet in the 

 Arbuckle Mountains of eastern Oklahoma (Wichita Mountains have 

 5,000 feet). Thence southwardly these deposits decrease rapidly in 

 thickness to central Texas, where, in Llano and Burnett counties, the 



