Id 



THE BRITISH ISLES. 



are to be preferred. Rising in hills and uplands of moderate elevation, they 

 are less exposed to changes of level and floods than continental rivers whose sources 

 lie in rocky mountains, covered during part of the year with masses of snow. 

 Wales and Scotland are less favourably situated in this respect. Their rivers, 

 unlike those of England, rise amongst elevated hills, and traverse narrow 



Y\s 10 —The River Basins of the British Isles. 



valleys, their rapid course being often impeded by ledges of rocks. The rain runs 

 quickly off the impervious rocks which occupy the greater part of their drainage 

 basins, and hence they are liable to sudden overflowings. All this renders them 

 unfit for navigation. The rivers of Ireland resemble those of England, in as far 

 as they generally flow through a flat country, are rarely rapid, and seldom inter- 

 rupted by cataracts ; but they differ from them in frequently traversing lakes. 



