PALAEOZOIC TIME. 229 



England. The eastern half of Vermont, as the rocks show, lay 

 within the submerged area ; and hence the emergence of the 

 western (or Appalachian) portion had been small. Lake Champlain 

 was probably defined as a long, narrow bay or arm of the St. 

 Lawrence sea. 



The disturbances opening the era of the Upper Silurian were 

 followed, if not attended, by the formation of a coarse conglome- 

 rate along the Appalachian region, which is described beyond. 

 There was also, as has been remarked, a nearly complete extermi- 

 nation of the living species over the continent. 



In Europe there was also a period of disturbance at the close of 

 the Lower Silurian ; but the destruction of life was less complete 

 than over central North America, and corresponds nearly with 

 that in the eastern basin about the Gulf of St. Lawrence. 



There is evidence of unconformability between the Upper and 

 Lower Silurian in some parts of England, and the elevation of the 

 Westmoreland Hills, as first ascertained by Professor Sedgwick, has 

 been referred to this epoch ; so, also, that of the mountains in North 

 Wales, and hills in Cornwall, and the range of southern Scotland 

 from St. Abb's Head, on the east coast, to the Mull of Galloway. 

 Elie de Beaumont refers to this era the elevation of the Hundsruck 

 Chain (now about 3000 feet high) and other ridges in Nassau. The 

 changes of the period are supposed to have been attended in 

 England by metamorphic action, in which gneiss and clay slates 

 were made out of the Lower Silurian deposits by some process 

 dependent probably in part upon the escaping heat of the epoch 

 of disturbance. 



B. UPPER SILURIAN. 



Marine life, large oceans, small lands, and warm climates — the 

 features of the Lower Silurian — continued to characterize the open- 

 ing period of the Upper Silurian. 



The periods and epochs indicated in the New York rocks have 

 been mentioned on p. 168. The periods are — the Niagara (5), the 

 Salina (6), and the Lower Helderberg (7). 



1. NIAGARA PERIOD (5). 



Epochs. — 1. Oneida epoch, or the epoch of transition between 

 the Lower and Upper Silurian, when the Oneida conglomerate (5 a) 

 was formed; 2. Medina epoch, or that of the Medina sandstone 



