1104 Proceedings of Royal Society of Edinburgh. [sess. 
35 m. ; it is the deepest of all known Icelandic lakes. It has two 
small islands, Sandey and Nesjaly. The bottom is, from the shore 
to the 10 m. curve, stone chips or dark volcanic sand, often covered 
with mud ; in the deepest part of the lake we find the mud absolutely 
predominant. This mud is of a dark, grayish-blue colour and con- 
sists chiefly of organic matter, especially diatom frustules. It is 
highly probable that the greater part of the water arises from springs 
in the bottom. 
According to Mr Soemundsson the surface tp. was, in the period 
from 16th July to 2nd August, 10 to 12, 2° C. The vegetation of 
higher plants along the shore is very poor ; on the other hand there 
is a luxurious growth of Characese ( Nitella ) in depths of 13 to 30 m. 
The rocks just beyond lake-level are covered with the gelatinous 
green alga, Tetraspora cylindrica. Insect larvae and Limncea are 
common near the shore. 
With regard to my own tp. explorations, I may refer the 
reader to the tp. curves and to the mean tp. for the months 
taken at the meteorological stations at Reykiavik and Storinupur. 
Monthly Mean tps. of the Air at Reykiavik 
and Storinupur. 
1902-1903. 
Reykiavik. 
Storinupur. 
July, .... 
11*1 
August, 
10-4 
September, 
9-2 
October, 
6*0 
November, 
3-5 
December, . 
1-2 
January, . 
-2*0 
February, . 
- 1*0 
-l’*9 
March, 
-1-6 
-2*2 
April, 
0-5 
-0*5 
May, .... 
5-5 
4-5 
June, 
8-8 
1 
8*5 
It will be seen that there, in spring, summer, and autumn, there is 
a fair conformity between the mean tp. of the month and the 
solitary observations taken of the atmosphere and of the surface 
water in the lake. On the other hand, it must be noted as a very 
remarkable instance, that during the entire winter no negative tp. 
