﻿136 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 22. 



That, with respect to movements of the earth's crust in this region, 

 during a period which geologists have agreed to consider as one and 

 indivisible, the oscillations have been great, both of depression and 

 elevation, and that there has been at several distinct periods a con- 

 stant return to a level very near the present one. The greatest amount 

 of elevation and depression does not seem to have been uniform : a 

 marked line of E. and W. physical structure has been least affected : 

 during the period of the greatest extension of the Northern Sea, the 

 amount of depression seems to have proceeded at a uniform pro- 

 gressive rate from S. to N., whilst with respect to the maximum of 

 elevation the increase was from E. to W. 



These former levels are to a great extent independent of the present 

 relation of land to sea : the external configuration of the country had 

 obviously been acquired prior to any of the successive conditions 

 which have been here described ; and the level of the sedimentary 

 deposits of the South of England, which rise to a line of 900 feet 

 above the sea, is simply the result of the last adjustment which has 

 taken place, and by which former inequalities have been placed in 

 common relation to the earth's curvature. 



