266 



Mr. W. H. Pearsall. 



(Table III). Finally, silts deposited from the lake waters are -uniformly 

 richer in potash than are the unaltered sands and glacial " clays " of the lake 

 floors, e.g., Nos. 2, 14, 16, Table III. 



Table III. — Proportions of Potash. 



No. 



Sand. 



Silt. 



Fine 

 silt. 





No. 



Sand. 



Silt. 



Fine 

 silt. 



£,0. 



5 



34 -2 



29 -3 



36 -5 



-0535 ■ 





10 



73-4 



19-2 



7-4 







•0290 



7 



69 -2 



14 -6 



21 -2 



0-0462 



I 



13 



71 -7 



14 -1 



14 -2 







-0260 



23 



44-9 



29-1 



26 -0 



-0410 



i| 9 



76 -6 



14 -0 



9-4 







-0232 



20 



51 -5 



28 -4 



20 -1 



0-0370' 





15 



82 -8 



15 -0 



2-2 







•0232 



6 



72 -0 



7-6 



20 -4 



0-0342 



\ 



11 



76 -8 



18 -0 



5-2 







-0228J 



8 



64-2 



23 -6 



12 -2 



-0338 





2 



63 -1 



16-1 



20-8 







-0220 ] 



19 



70-9 



14-1 



15 -1 



-0336 





14 



78-0 



10-9 



11-1 







-0210 \ a 



12 



65 -3 



24-5 



10 -2 



-0301 





16 



75 -1 



14-8 



10 -1 







•0202 J 



Figures as percentages, a, Boulder clay -with slight silt ; h, slight silt orer stones. 



Hence it may be inferred that fine silts adsorb potassium from the lake 



waters, resulting in a decrease in the ratio ^^^P"t"F^P as the lake becomes 

 ° CaO + MgO 



more silted. It may be noted that the adsorption of K would be accompanied 

 by a liberation of Ca and Mg into solution. 



The increase of carbonates, nitrates and silica in the silted lake-waters is 

 apparently due also to the effects of silting. The development of soil in the 

 drainage system and of silts in the lakes may be assumed to be followed, in 

 each case, by the development of vegetation. Organic matter deposited is 

 then decayed under the aerobic conditions of the soil, forming CO2 and 

 nitrates. If the soils are rich in bases, complete decomposition results instead 

 of the partial disorganisation which results in the formation of peat. 

 Similarly sub-aqueous silts rich in potash are characterised by organic 

 matter decaying rapidly and completely, while coarser potash-poor silts 

 accumulate organic matter which is relatively undecayed. (Nitrates are 

 formed in potash-rich silts.) It is apparently correct, therefore, to assume 

 that the adsorption of potassium by silts results in the acceleration and 

 completion of the processes of decay, and the formation of increased quantities 

 of CO2 and nitrates, the end products of these processes. Thus it follows that 

 the silted lake waters contain greater quantities of carbonates, nitrates and 

 usually of organic matter, and we can probably attribute their higher propor- 

 tions of silica, calcium and magnesium, in part, to the solvent action of CO9. 



(There is, of course, a resultant decrease in the 



NasO + KsO 



ratio.) Thus 



CaO + MgO 



clearly the main differences between the lake waters are closely related to 

 the degrees of silting of the lakes. 



