122 HOBBS— CHARACTERISTICS OF THE [April 22, 



extension of the same ice tongues.^"' In these cases the ice fronts 

 of the glaciers are cut back into cHffs from which are derived the 

 bergs that float upon the surface. The ice cHff and some of the 

 bergs of Lake Argentino are shown in Plate XXX, B. According 

 to Moreno, Lake Tyndall is bounded on the west by true inland-ice, 

 the remnant of the larger sheet of Pleistocene times. 



Ice Dams in Extraglacial Drainage. — In north Greenland out- 

 side the ice front, the brooks sometimes offer a striking example 

 of ice obstructions forming by irrigation. This is often the case 

 where their beds are wide and are covered with boulders. The 

 water generally continues to run beneath the stones for a great 

 part of the winter. Later, however, its outlets may freeze up, 

 whereupon the water rises, inundating the stones and covering them 

 with an ice crust. Through successive obstruction, overflowing 

 and freezing of these streams, the ice dam which results may attain 

 to such a thickness that it is still to be found at these places late in 

 the summer when the ice and snow have elsewhere disappeared 

 from the low land."^ The significance of such dams as obstruc- 

 tions during a readvance of the ice front may well be considerable. 



Submarine Wells in Fjord Heads. — Rink states that the sea flow- 

 ing into the fjord in front of the glacier tongue which ends below 

 the water level, is kept in almost continual motion by eddies not 

 unlike those which are seen where springs issue from the bottom 

 of a shallow lake. Such areas upon the surface of the fjord may 

 generally be recognized by the flocks of sea birds which circle above 

 them and now and then dive for food.^^- The existence of such 

 fresh water streams as this implies may also be inferred from the 

 strong seaward current that prevails in the fjords and which is so 

 effective in clearing them of bergs. Such a whirlpool of fresh 

 water or " submarine well " was observed by Rink in the Kvanersok- 



"" Francisco P. Moreno, " Explorations in Patagonia," Geogr. Jour., Vol. 

 14, 1899, pp. 253-256. Also Hans Steffen, " The Patagonian Cordillera and 

 its Main Rivers between 41° and 48° South latitude," ibid.. Vol. 16, igoo, pp. 

 203-206. Also Sir Martin Conway, " Aconcagua and Tierra del Fuego," 

 London, 1902, pp. 134-135. 



"^ Henry Rink, " Danish Greenland, Its People and its Products," Lon- 

 don, 1877, p. 366. 



""Rink, /. c, pp. 50, 360-363. 



