STUDIES ON THE VEGETATION OF ICELAND 7 
fortunately there are no records from the highlands. The number 
is probably considerably higher here. 
Precipitation. The precipitation in summer is principally rain, 
in winter principally snow. The annual precipitation is greatest to 
the south and east, decreasing towards the west and being compa- 
ratively small in the north. 
In the Vestmannaeyjar the annual precipitation is 1319 mm. (see 
table 1), distributed over 207 days, in East Iceland it is 1117 mm., 
distributed over 146 days, in West Iceland, Stykkishölmur, the amount 
of precipitation is already considerably lower, 662 mm. distributed 
over 117 days. From the highland tracts we have unfortunately no 
investigations on the amount of precipitation for the whole year, so 
it is impossible to draw any comparison with the coastal stations. 
The number of days with precipitation for Möörudalur is 153, thus 
somewhat higher than for Grimsey, corresponding fairly well with 
East Iceland. It may, however, be taken for granted that the amount 
of precipitation is not nearly as great in the highland tracts as at 
the coast. Observations from some of the summer months at a 
highland station, Grimsstadir, about 385 m above the sea, in the 
vicinity of Médrudalur, show an average monthly value for the five 
months May—September of 26.8 mm, while the average monthly 
amount of precipitation for Grimsey for the five months is 31.4 mm. 
The amount of precipitation and the number of days with pre- 
cipitation are highest in the autumn and winter months, lowest in 
spring and summer. This applies especially to the regions to the 
south of glaciers. 
In winter the precipitation occurs principally in the form of 
snow, though with a difference in the different parts of the country. 
Table 1 shows the number of days with snow for the different 
stations where this has been investigated. In the highland tracts 
and the north country snow predominates, in the south there are 
comparatively few days with snow; while snow is rare here in the 
summer, it is more frequent in the north. In the highland tracts 
snow in summer is even the rule. At Môdrudalur the average monthly 
number of days with snow in summer is 2—4. 
Unfortunately there are no observations on the depth and du- 
ration of the snow-covering in the various regions of Iceland. As 
to the depth of the snow-covering Thoroddsen states that it varies 
much with the situation and the altitude above the sea, and from 
one year to another. As to its duration he states that the snow 
