Freshwater Life in North-East Greenland. 327 



land, on Ihe often Tertile, low stretches, which at many places lie 

 between the inland hills and the sea. Owing to their situation it 

 will readily be understood, that the extent of these lakes is depen- 

 dent on the season of the year, the amount of the winter's snow, 

 presence of outlet and inlet or not, and on their size and depth. 

 hi winter these water-basins are often never suspected, covered as 

 they are by meter-thick ice and with snow, which makes them 

 level with the surrounding land (the thickness of the ice measured 

 reached about 2 meters). When the snowfall of the winter is not 

 specially great and the early part of summer is warm (i. e. many 

 sunny days), the snow may have melted along the banks of the 

 lakes and ice-free water found here already at the end of May, even 

 though owing to the frost at nights the water is covered by thin 

 ice for most of the day (Hvalrosodden, May 1907); on the other 

 hand, if there is much snow in winter and a good deal of fog in 

 early summer, the banks of the lakes are not free of ice before 

 the middle of June (Skibshavnen, 1908). But when the melting has 

 once begun seriously, it can be watched spreading daily, until after 

 8—10 days most of the lakes are free of ice, all the more rapidly 

 if the lake is small. For a couple of months the lakes are now 

 open, until the night frost at the end of August becomes severe 

 enough to form thin ice by the banks; gradually the ice spreads 

 over the whole lake and from the middle of September the ice is 

 so thick, that even the outlets cease to How. The icy covering of 

 the lakes in winter corresponds in thickness to the average temper- 

 ature [in 1906 — 07 the winter was more severe than in 1907 — 08 

 and the thickness of the ice was thus different (ca. 24-2 and ca. 2 

 meters)]; the size and depth of the lake and the, in consequence, 

 stronger or weaker currents in the water have certainly some impor- 

 tance also. Thus, all the lakes and pools which are shallower than 

 ca. 2 meters are frozen to the bottom in winter — a condition 

 which, taken in conjunction with the absence of openings and 

 channels in the ice, makes it the more remarkable, that various 

 animal forms are able to live, though the air has no access to the 

 water, and even to become frozen-in in the mud (Entomostraca). 



In the littoral region, that is near the banks of the lake, the 

 hydrographical conditions are naturally extremely variable. Here 

 the power of the sun is greatest (owing to the surrounding, dark 

 land and the shallow depth, so that the bottom gets warmed up); 

 but it is also here that the autumn frost hrst forms the thin ice, 

 which often thaws in the day-time (at the beginning). The time of 

 day at which the temperature of the water is taken is also of great 

 importance, as also the temperature of the air and the weather. 



