274 



Mr. W. H. Pearsall. 



depths of 3 or 4 m. These wave-washed areas can only accumulate silt 

 during calm weather, and hence change their character very slowly. Thus 

 the discharge of ore washings into these lakes would cause an abundance of 

 fine silts in deep water, and this would result in the replacing of Nitella by 

 Potaraogeton spp. On the other hand, the shallower water soils would remain 

 little altered, and would retain their primitive vegetation of Isoetes. Another 

 factor tends to accentuate the retention of this primitive shore line in 

 Ullswater and Coniston. The shores are relatively straight, as compared with 

 Windermere and Derwentwater, and hence, offering no obstacles to the 

 sweep of waves and littoral currents, are kept comparatively silt-free at 

 depths of less than .3 to 4 m. 



Shallow- Water Vegetation. — In the case of the shallow-water plants, much 

 greater difficulty is experienced in making a comparative table of distribu- 

 tion. These plants are directly affected by wave action, and they are 

 therefore very closely dependent upon the degree of exposure of the lake 

 shores. In lakes like these, varying greatly in size, orientation and shelter, 

 a direct numerical comparison is therefore impossible, and only the presence 

 or absence of typical plant communities can be given : — 



Table YI. — Distribution of Shallow-water Plants. 















o 



ID 





. 



p 









astwater. 



merdale. 



ittermere. 



M 

 <a 

 o 



g 

 s 



rwentwat 



m 



■ssentliwa 



niston. 



s 

 a 



.3 



? 



-.^ 









PQ 



o 



a> 

 Pi 



w 



ca 



m 



o 

 Q 











+ 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



+ 













+ 









+ 



+ 



+ 













+ 



+ 



+ 



+ 



+ 



+ 



+ t 

















+ 



+ 



+ 



+ 



+ 











+ 



+ 



+ 



+ 



+ 



+ 



+ 















+ 





+ 



+ 



+ 





+ 











+ 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



Carex inflata, Huds / 





+ 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



* Potamogeton gramineus, L. (agg.), x P. nitens, Weber., P. perfoliatus, L., P. alpinus, Balb. 



t M. alternijlorum, D.C. 



J Including occasional Castalia minor, D.C. 



§ Nymphxa lutea, L., and Castalia alba. Wood. 



Even tills rough method of comparison indicates that shallow-water plants 

 are more typical of evolved than of primitive lakes, in spite of the con- 

 siderable variations observed. Derwentwater, with a broken shore-line and 

 numerous islands, is comparatively rich* in this type of vegetation, and of the 



