400 PROF. J. PRESTWICH (W THE GLACIAL PERIOD, WITH 



mary has recently been given by Dr. Sink *. Their observations 

 fully confirm those of Professor Helland, and show that the motion 

 of the inland ice may be compared to an inundation. It was found 

 that there is a general movement of the whole mass of the ice 

 from the central regions towards the sea, and that it concentrates 

 its force upon comparatively few points in the most extraordinary 

 degree. These points are represented by the so-called ice-fjords, 

 through which the annual surplus of ice is carried off and discharged 

 in the shape of icebergs. 



The velocity of the ice was noted in seventeen glaciers, the 

 measurements being repeated during the coldest and the warmest 

 seasons; and it was found, remarkable as it may seem, that the 

 movement was not materially influenced by the seasons. The great 

 glacier of the ice-fjord of Jakobshavn, which has a breadth of 4500 

 metres, was rated at 50 feet per diem. One of the glaciers in the 

 ice-fjord of Torsukatak has a movement of between 16 and 32 feet 

 daily. The large Karajak glacier, about 7000 metres broad, proceeds 

 at the rate of from 22 to 38 feet in twenty-four hours ; and another 

 in the fjord of Jtivdliarsuk, 5800 metres broad, at from 24 to 40 

 feet. The conclusion at which the Danish corps arrived was that 

 the glaciers which produce the bergs move at the extraordinary rate 

 of from 30 to 50 feet per diem throughout the year. 



What, then, may have been the rate of movement of the great 

 ice- sheets of America and Europe in the Glacial epoch ? ~No doubt 

 the velocity of the ice in the ice-fjords is increased by the free play 

 of the ice as it reaches the sea and by the rapidity with which the 

 bergs are detached. It is also increased by the circumstance that 

 the great body of inland ice, the whole of which is in motion, is 

 forced, and has to escape, through the passes between the range 

 of mountains which fringe the coast and rise high above the imme- 

 diately inland districts. The summits of those mountains rise in 

 bare isolated masses (Nunataks) above the surrounding ice-sheet, 

 and the passes between them and through which the ice has forced 

 its way have been gradually worn down, and now form the channels 

 (fjords) through which the surplus inland ice escapes, with a velo- 

 city increased in proportion to the contraction of the passages. 

 Thus in the ice-fjord of Torsukatak, which is nearly 5 miles wide, 

 the ice passes out with a mean velocity of 24 feet per diem, or 

 equal to a mass of ice of that width, and If mile long, annually ; 

 the Karajak glacier, which is 4^ miles broad, flows at the rate of 

 30 feet daily, or equal to a length of above 2 miles a year ; and in 

 the huge ice-fjord of Jakobshavn, which is not quite 3 miles broad, 

 the ice attains a velocity of 50 feet daily, so that a length of above 

 3 miles of ice is discharged annually. 



Until all the glaciers have been gauged, and we know the relation 

 of their totals to the breadths of the intervening " Nunataks," no 

 definite measure of the total volume of annual surplus ice can be 

 established ; but for our general purpose some approximate idea 

 may be formed. The average of the great glaciers gives a mean rate 

 * Trans. Edinb. Geol. Soc. vol. v. p.;2S6 (1887). 



