The Development of Vegetation in the English Lakes. 



265 



Bassenthwaite, and Hawes Water remain as intermediate examples between 

 the two extremes. Other attributes of these lakes will now be considered. 



Chemical Characters of the Lake Waters. 



Chemically the waters of these lakes possess much in common (see 

 Appendix II). They are notably poor in dissolved minerals, and particularly 

 in calcium and carbonates. Other ions, therefore, constitute an unusually 

 large proportion of the dissolved matter, particularly those of the alkalies 

 (Na and K), an unusual feature in pure natural waters. The sulphate- 

 content is high in the case of Crummoek, Buttermere, Bassenthwaite, and 

 Esthwaite, the only lakes where drainage systems lie entirely on the Skiddaw 

 and Silurian rocks. In other respects, the influence of various strata is not 

 very apparent and the only satisfactory classification is obtained by arranging 

 the lakes in the two groups, rocliy and silted^, as already distinguished. It 

 then appears that: — 



(1) The waters of the rocky lakes have a high ratio of ^^^P "^^l^^P - 

 ^ ' ^ ^ CaO + MgO 



(2) The waters of silted lakes are characterised by larger quantities of 

 nitrates, carbonates and silica. 



(3) The latter waters tend also to possess larger proportions of lime and 

 organic matter. 



All the variations thus observed between the two types of water can 

 apparently be related to the physical differences in the lake-basins and their 



drainage systems. The ratio ^ is chosen to represent the difference 



^ CaO-hMgO ^ 



in the character of the bases. The tendency for the ratio to be low in silted 



lakes is probably in part due to the adsorption of K by sediments. The 



following facts bear out this assumption. While in Ennerdale and Wast- 



water potassium constitutes 50 to 60 per cent, of the whole K-Na residue, in 



Esthwaite and UUs water it rarely exceeds 20 per cent. It is, moreover, well 



known that the drainage water from normal soils rarely contains much K, 



owing to the adsorption of this ion by the electro-negative soil colloids, and 



the same effect is produced when soil particles {i.e., silts) are suspended in 



water containing traces of potassium. It has been shown already that the 



silted lakes are surrounded by greater areas of fertile soil, and possessed of 



greater quantities of suspended matter in their waters, and it may therefore 



be assumed that greater quantities of potassium are adsorbed by silts from 



the waters of these silted lakes, in comparison with those of rocky lakes. In 



addition, silted lakes possess finer sediments than rocky ones, and it is found 



that the finer silts contain larger proportions of potash than the coarser 



