Dakin and Latarche — The Plankton of Lough Neagh. 25 



Thus it will be seen that Lough Neagh water is not derived from areas 

 corresponding to older Palaeozoic outcrops. The following table, taken from 

 the Eeports on the Bathymetrical Survey of the Scottish lochs, shows the 

 composition of the water of Lough Neagh and three other lakes for purposes 

 of comparison: — 



Analysis of Lake Water. 



Dissolred Matter 

 in parts per thousand. 



Lough. Neagh, 

 0-155. 



Lake Geneva, 

 0169. 



Lake Champlain, 

 0-067. 



Lake Baikal, 

 0-069. 



Percentage Composition 

 of Dissolved Matter. 



Ca 



17-7 



27-8 



21-2 



23-4 



Mg . 



1-3 



4-0 



4-2 



3-0 



Na 



15-4 



1-2 



S-8 



5-8 



K 



— 



0-9 



— 



3-4 



Cos 



36-9 



37-3 



45-8 



49 8 



CI 



5-7 



0-6 



1-8 



2-4 



SO4 



10-7 



25-7 



11-0 



6-9 



Si02 



3-3 



■ 2-0 



5-6 



2-0 



(AlFe)203 



6-7 



trace 



1-6 



1-4 



It will be noticed that the Lough Neagh water contains an exceptional 

 amount of sodium, chlorine, and iron. The presence of sodium chloride is 

 probably due to wind-blown salt from the sea. We have already seen that 

 the lake is situated not far from the sea ; and its surface exposed to the air is 

 probably greater in proportion to the total volume of water than in most lakes 

 of its size in the world. 



The range of temperature of the water of Lough Neagh throughout the 

 year is very great. This is what one would expect in a lake of such great area 

 and slight depth. There is a great contrast here with the Scottish lakes, 

 whose annual temperature- variation is only about 5-15^ C. The summer 

 temperature of these Scottish mountain-lakes is not high ; and in many cases 

 the water does not freeze during the winter. Lough Neagh has been frozen 

 on several occasions in recent years, and to an extent to permit of skating. 

 During that part of the winter falling in the peiiod of our observations, the 

 temperature of the air was rather mild in north-east Ireland, and the water 

 of the lake did not freeze. During the summer a temperature of 20° C. is 

 recorded; and this must have been far exceeded during the summer of 1911. 

 The temperatures of the surface water are as follow : — 



