90 HOBBS— CHARACTERISTICS OF THE [April 22, 



Peary has referred to these dimples on the surface of the inland- 

 ice as " basins of exudation," and has compared the cross profile 

 in its ups and downs to that of a railroad located along the foot- 

 hills of a mountain system.*** In his earlier reconnaissance of the 

 isblink from near Disco Bay, Peary describes such a dimple above 

 the Jakobshavn ice tongue " stretching eastward into the ' ice-blink,' 

 like a great bay," as a feeder basin.*^ The exact form of such 

 dimples upon the ice surface is well brought out in von Drygalski's 

 map of the Asakak glacier tongue on the Umanak Fjord (see Fig. 

 22, p. 82).-*^ 



We may easily account for the existence of these dimples by 

 drawing a parallel from the behavior of water as it is being dis- 

 charged from a lake through a narrow and steeply inclined channel. 

 Under these circumstances the surface is depressed through the 

 indrawing of the water on all sides to supply the demands of the 

 outflowing current. That within the upper portions of the glacier 

 tongues of the Greenland isblink the ice flows with a quite extra- 

 ordinary velocity has long been known. Values as high as 100 

 feet per day have been determined upon the Upernavik glacier.*-* 

 By more accurate methods, von Drygalski has obtained on one of 

 the ice tongues which descends to a fjord, a rate of about 18 meters 

 or 59 feet in twenty-four hours.*^ Upon the inland-ice some dis- 

 tance back from the head of the fjord, on the other hand, a rate 

 was measured of only one to two centimeters per day. 



Scape Colks and Surface Moraines. — The velocities of ice move- 

 ment which obtain within and about the heads of the glacial tongues 

 are, there is thus every reason to believe, as different as possible 

 from the ordinary general outward movement of the inland-ice. 

 Within this marginal zone areas of exceptional velocity of the 

 inland-ice are likely to be found wherever its progress is interfered 

 with by the projecting nunataks. Just as jetties by constricting 



^ Geogr. Jour., Vol. 11, p. 232. 



*^Jour. Am. Geogr. Soc, Vol. 19, 1887, p. 269. 



^ " Gronland-Expedition," /. c, map 7. 



^^^ Lieut. C. Ryder in 1886. Helland on a glacier of the Jakobshavnfjord 

 found a rate of 64 feet daily. 



■" E. von Drygalski, " Die Bewegung des antarktischen Inlandeises," 

 Zeitsch. f. Glctschcrk, Vol. i, 1906-7, pp. 61-65. 



