LOWER SILURIAN. 217 



It is not yet known that any portion of the Appalachians from 

 New Jersey southwestward participated in the disturbances of this 

 epoch. But, according to Safford, Newberry, and Orton, the region 

 from Lake Erie over Cincinnati into Tennessee, where rocks of the 

 Hudson River and Trenton eras are exposed to view, was then, for the 

 most part, raised above the sea-level, and so remained, through the rest 

 of the Silurian age and part of the Devonian, as an island in the con- 

 tinental seas. The axis of the uplifted region is parallel to that of 

 the Appalachians. That this was the time of the uplift is proved by 

 the absence of Upper Silurian and Lower Devonian beds over the 

 region, these formations thinning out toward the axis ; and, in Ten- 

 nessee, as Safford states, by the Devonian black slate resting directly 

 on the Lower Silurian beds. Over Kentucky, the uplift was less than 

 in Tennessee or Ohio, and the area of it may have remained sub- 

 merged. In Ohio, the region reaches Lake Erie between Sandusky 

 and Toledo, and from there southwestward, it is marked, as Professor 

 Newberry observes, by a distinct arch in the strata. The line of the 

 axis presents now no conspicuous topographical feature ; but the di- 

 rection of the draining streams, which follow the strike of the strata 

 on either side, indicates that it once formed a watershed that gave the 

 initial bearing to their flow. The part of the arch about Cincinnati 

 has been more deeply and extensively removed than farther north, 

 though higher now than elsewhere, and, therefore, " this probably was 

 originally the highest part of the arch within the limits of the State 

 of Ohio." 



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

 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 many parts of England ; and the elevation of the 

 Westmoreland Hills, as first ascertained by Prof. 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 3,000 feet high) and other ridges in Nassau. The changes 

 of the period are supposed to have been attended in England by meta- 

 morphic action, in which gneiss and clay slates were made out of tho 

 Lower Silurian deposits- 



