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CHAPTEE XXXII. 



QUALITIES OF RIVER-WATERS DISSOLVING OF LIMESTONE 



ROCKS BY SOLUTION. 



I HAVE already given a sketch of the chief river areas 

 of Great Britain, but I did not enter upon one 

 important point connected with them, namely, the 

 qualities of their waters. If we examine the geological 

 structure of our island with regard to its watersheds 

 and river-courses, we find, as already stated, that the 

 larger streams, with one or two exceptions, run into the 

 German Ocean ; the chief exception being the Severn 

 and its tributaries, which drain a large proportion of 

 Wales, and a considerable part of the interior of 

 England. A much larger area of country is, however, 

 drained towards the east than to the west. 



When we examine the qualities of the waters of our 

 rivers, we find that this necessarily depends on the 

 nature of the rocks and soils over which they flow. 

 Thus the waters of the rivers of Scotland are, for the 

 most part, soft. All the Highland waters, as a rule, 

 are soft ; the mountains being composed of granitic 

 rocks, gneiss, m'ica-schist, and the like, a very small 

 proportion of limestone being intermingled therewith, 

 and the other rocks being, for the most part, almost 

 free from carbonate of lime. Only a small proportion 

 of lime, soda, or potash, is taken up by the water that 

 falls upon, flows over, or drains through these rocks, 



