130 HISTORICAL GEOLOGY 



The eastern interior sea was probably connected with the Gulf 

 on the south, and with the Atlantic, through the St. Lawrence 

 Basin, on the north. 



Late Devonian. — During late Devonian (Senecan and Chau- 

 tauquan) time the relations of land and water were much the same 

 as during middle Devonian, with the following principal differences: 

 The eastern and western interior seas became connected; the 

 southern Appalachian region became submerged; and the connec- 

 tion with the Gulf of Mexico appears to have been closed. In 

 New York and the northern Appalachian region, there was a tre- 

 mendous accumulation of sandstone together with more or less 

 shale and conglomerate. The Chemung-Catskill formation, as 

 already stated, is largely a shallow-water, non-marine deposit from 

 1500 to 8000 feet thick in New York and Pennsylvania. The few 

 known fossils are non-marine types. This, together with the 

 common occurrence of red shales and sandstones, and the great 

 thickness of the beds, all point to the origin of this remarkable 

 formation as either a great delta deposit pushed out into the 

 shallow interior sea, or as an estuarine or lagoon deposit. Notable 

 thinning toward the west proves the material to have come from 

 the east, doubtless from greatly rejuvenated Appalachia. Farther 

 westward, over Michigan, Indiana, and Tennessee, the deposits 

 formed at the same time were mostly shales, usually not over a 

 few hundred feet thick. 



Close of the Devonian. — Throughout most of North America 

 there was a quiet transition from the Devonian to the succeeding 

 Mississippian, therefore the two systems are not sharply separated. 

 In Maine, Nova Scotia, and New Brunswick, however, the strata 

 were considerably upturned and eroded toward the close of the 

 Devonian, and Mississippian rocks rest upon them by unconformity. 



Foreign Devonian 



Europe. — It may be said in general that the Devonian of 

 Europe began with a progressive transgression of the sea, con- 

 tinuing till near the close of the period when much of the continent 

 was submerged as shown in Fig. 72. This extensive sea spread 

 over the barrier which, since Cambrian time, had quite effectually 

 kept Europe divided into two provinces (a northern and a southern) 

 or basins of deposition. 



