322 SUMMARY OF GEOGRAPHICAL EVOLUTION. [CHAP. XIV. 



these circumstances would enable the sea to creep up the 

 valleys of the two rivers, and eventually to submerge part 

 of the low watershed between them ; waves and currents 

 would soon widen the breach, and have continued to widen 

 it from that time to the present day. 



Thus was Britain finally separated from the Continent 

 to which it had been united throughout the greater part 

 of Tertiary time, and thus was the geographical evolution 

 of the British Isles at length accomplished; for though 

 certain minor changes took place after the formation of 

 the Straits of Dover, yet this severance of England from 

 the Continent gave Britain the geographical position she 

 now holds, and must therefore be regarded as the final act 

 in the long series of operations which conduced to the 

 building and fashioning of the British Isles. 



Under the combined effect of subsidence and marine 

 erosion the British coast-lines continued to recede after 

 the formation of the Straits of Dover, but when after a 

 time the subsidence ceased, recession proceeded at a much 

 slower rate, and only along those shores which were ex- 

 posed to the direct action of currents, while the loss so 

 caused was partially counterbalanced by the silting up of 

 bays and estuaries. In Scotland, moreover, a vertical up- 

 heaval of nearly 50 feet resulted in an important accession 

 of land. The present outline of the British coast is there- 

 fore the outcome of all these minor operations, the balance 

 of gain and loss being apparently very nearly equal in the 

 case of Scotland, but decidedly on the side of loss in the 

 south of England. 



Minor geographical changes are even now in progress, 

 and there is no reason to suppose that the present arrange- 

 ment of land and sea is the final geographical condition 

 of Europe, or that the British Islands will never again be 

 subjected to movements of upheaval and depression like 

 those which they have experienced in the past. It is very 



