Ii6 TVesi;: Phytoplankton of English Lake District. 



ated within a radius of about 15 miles from a centre, taken at 

 Dunmail Raise (about half-way between Grasmere and Thirl- 

 mere). Within this area many high mountains are embraced, 

 four summits being over 3000 feet, and four others exceeding 

 2900 feet. In all, there are more^than forty mountains over 

 2000 feet in height in this small area. 



The lakes are numerous, and ten or twelve of them are 

 moderately large, although rather narrow,|Windermere having 

 a length of over ten miles, Ullswater a length of over seven, and 

 Coniston Water a length of over five miles. There are at least 

 a dozen more smaller lakes, no less important than the larger 

 ones from an algological standpoint, and in addition, a con- 

 siderable number of mountain tarns. 



As might be expected in a western mountainous region, the 

 rainfall is very heavy, varying from about 50 inches in the 

 outer zone, to about 150 inches in the more central region of 

 the highest mountains. The rainfall at Seathwaite at the 

 upper end of Borrowdale, is the heaviest in the British Islands, 

 and is only approached by that registered in the Cullin Hills in 

 Skye. This heavy rainfall, and the frequent torrential character 

 of it, is no doubt responsible for washing many of the bog 

 species of Algse into the plankton, and affords an explanation 

 of the presence of certain species in the limnetic region of the 

 lakes. 



We hav^e already pointed out the important relationship 

 between the geological character of a district and the con- 

 stituents of its Alga-flora, more especially of its Desmid-flora.* 

 The entire Lake District is an Older Palaeozoic area, in which 

 a northern outcrop of Ordovician strata is separated from a 

 southern Silurian outcrop by an extensive mass of pre-Devonian 

 igneous material. The really rich Alga-floras are all on the 

 Older Palaeozoic or Precambrian areas, and the English Lake 

 District possesses a richer Alga-flora than any other part of 

 England, although not quite equal to that of the north-west of 

 Scotland or the west of Ireland. The phytoplankton of the 

 lakes is similarly rich in species, although not so prolific as the 

 limnetic flora of the lakes of north-west Scotland. 



* W. and G. S. West, ' Alga-flora of Yorkshire,' ' Trans. Yorks. Nat. 

 Union,' V., 1900-1901, p. 5 ; G. S. West, ' Treatise on British Freshwater 

 Algae,' Cambridge, 1904, p. 6 ; W. and G. S. West, ' A further Contribution 

 to the Freshwater Plankton of the Scottish Locks,' ' Trans. Roy. Soc, 

 Edin.', XLI., Part III., 1905, p. 511. 



Naturalist. 



