PALEOZOIC TIME — UPPER SILURIAN. 537 



northeastward across the present Gulf of St. Lawrence to Newfoundland j 

 for it has been shown by Canadian geologists that the Upper Silurian fossils 

 within the Acadian trough in Nova Scotia are not all of American type, but 

 have many relations to those of Great Britain, much closer relations than 

 the fossils of the island of Anticosti. The fact would put Anticosti within 

 the Gaspe-Worcester trough. But such a coniine could not have been an 

 uninterrupted barrier, since the troughs of the Connecticut valley and Gaspe- 

 Worcester belt must have had tidal connection with the Atlantic. 



The two large islands of the Cincinnati uplift are those marked C and T. 

 They partially divide off from the great Continental Interior a portion called 

 the Eastern Interior Sea, which from this time onward was like a great bay, 

 having a narrow southwest opening over Alabama, a length of about 700 

 miles, and its northern limits near the sites of Albany and Troy. Its waters 

 communicated, in the Upper Silurian era, with those of the Central Interior 

 Sea, over Michigan and northern Ohio. But this connection was diminished 

 during the progress of Paleozoic time. It had probably, also, a shallow 

 connection with the Atlantic over Pennsylvania and Maryland, where the 

 land is now low, permitting of an interchange of water and life. 



The conditions of this Eastern Interior Sea influenced not only its tides 

 and currents, but also the temperature and purity of the waters, the supply 

 of sediments, the kinds of life, and hence in various ways modified rock- 

 making and biological distribution. And this influence was all the more 

 profound that the eastern part of the great bay was within the limits of the 

 slowly deepening Appalachian trough, or geosyncline, in which thick deposits 

 were in progress for the future Appalachian Range. 



West of the Mississippi there was another island, that of Missouri. 

 Probably Upper Silurian beds exist to the south of it, according to recent 

 observations by H. S. Williams. But farther southwestward, over much of 

 Arkansas and over Texas, to the Pecos (R. T. Hill), Upper Silurian and 

 Devonian beds are absent ; and it is probable that a large area of dry land 

 here existed. Its limits, however, are so uncertain that it is not indicated 

 on the map. Moreover, Silurian and Devonian beds have not yet been 

 reported from Mexico, and the Carboniferous are the only Paleozoic beds. 



The dry land of the continent was small, and hence there were only small 

 streams for the supply of sediments. Among them an embryo Hudson liiver 

 brought down Adirondack waters and detritus to the head of the Eastern 

 Interior Sea, near Albany, and an embryo Mississippi and a St. Lawrence 

 drained other Archaean areas. 



The rock-making of the period was confined, so far as has been ascer- 

 tained, to the Interior Continental Sea and the troughs or channels of New 

 England and eastern Canada. These troughs are those of Archaean origin, 

 already reported : commencing to the eastward, the Acadian, the Gaspe- 

 Worcester, the Connecticut valley, and, during the later part of the period 

 only, the Hudson-Champlain trough. No Upper Silurian beds are known 

 along the Atlantic border south of New York. 



