CHAPTEE XIX. 



GEOLOGICAL REVOLUTIONS. WASTE OF THE EARTH'S 

 SURFACE BY THE SEA AND ATMOSPHERE. 



THE land and sea of Britain had acquired the nearly settled 

 condition in regard to limits, levels, and climate, which we now 

 behold, when first the rude inhabitants gave signs of humanity by 

 inventions to meet the wants of barbarian life. How this condition 

 had been attained ; what a long series of physical changes had 

 visited every point of the area ; how repeated were the movements ; 

 how frequent the alternations of wasting lands and refilled sea-beds, 

 is the subject of geological history. Never-ceasing action from 

 within to raise or depress, ever-recurring vicissitude from without 

 to waste what had been raised and to heap fresh matter in the 

 sea-bed which had sunk, these unquiet agencies are still at work 

 to break the repose of nature; but their power is weakened, and 

 a thousand years of ordinary processes pass and seem to leave no 

 monuments of change worthy of being counted among the ' revo- 

 lutions of the globe/ Yet in a period comparatively modern, ac- 

 cording to geological chronology, a change has taken place in the 

 northern regions of the globe, on a scale hardly to be surpassed 

 by any earlier ' cataclysm.' For it is no longer as a plausible 

 hypothesis, but as a theory founded on a connected history of real 

 occurrences, that we admit of the doctrine of a general cooling of 

 our now temperate regions to the condition of Greenland, accom- 

 panied by great rising and falling of continents and sea-beds, since 

 the now living races of plants and animals came into existence. 

 The land is believed to have been covered with snow and glaciers ; 

 next, to have been depressed 1000 or 1500 feet below its present 

 standard, when shells of the old sea-shore were left on the sides 



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