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THORODDSEN 



The drift-ice also carries to the coast of Iceland fragments of rock 

 which are not found in Iceland (gneiss, granite, talc-slate, mica- 

 slate, etc.), and also gravel, clay and earth from other Arctic coun- 

 tries. Moreover, the warm water of the Gulf Stream sometimes carries 

 drift-material with it from southern parts, e. g. mahogany, sugar- 

 cane, "nuts" of Entada Gigalobinm, Miicuna urens, Guilandina Bon- 

 diicella, etc. 



The weather of the North Atlantic Ocean depends upon the 

 winds, which also exercise a great influence upon the currents 

 around Iceland. The mean atmospheric pressure in the North At- 



Fig. 20. Seeds of Entdda fni/alohiuin (1), Mucitna urens (2), and Gnilandhut Bonducdla (3). 



lantic is generally lowest to the south-west of Iceland but there is, 

 in addition, another centre of low barometric pressure north-east 

 of Iceland; on the whole, the direction of the winds over Iceland 

 is determined by this. In West and North Iceland the majority of 

 the winds blow from SE., E. and NE., while on the east coast 

 winds from the NE. and NW. are nearly equally numerous (20 % 

 and 17 % relatively) because here both the above-mentioned centres 

 of low atmospheric pressure try to prevail. This is true of the 

 average condition only, because in reality the wind-conditions from 

 day to day are very variable, as the ocean here is constantly visited 

 by moving centres of depression. The barometer in Iceland is subject to 

 very great changes. In Reykjavik the barometer, during a period of 

 28 years, has oscillated between 789 mm. and 697 mm.; at Stvkkis- 



* 



holm, dining one of 33 years, between 789 mm. and 700.3 mm.; in 

 the Veshnannaeyjar during a period of 29 years, from 789 mm. to 



