Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/186

148 148 AMTTND HELLAND ON THE FJOKDS, LAKES,

rises and falls with the tide : this ice enables one to reach the glacier and the side of the main fjord. The surface of the glacier is greatly crevassed, some of the ice-peaks being full fifty feet high ; still the glacier can be traversed up to a distance of about, a hundred paces from the side of the fjord : here, however, it is broken up into steep inaccessible crags by gaping crevasses fathoms broad, which run in all directions. To this glacier there is no continuous lateral moraine, but erratic blocks and dirty ice occur on its surface near the margin. As a rule, no boulders were seen in the middle part of the glacier.

The breadth of the fjord varies ; in one place which was measured it was about 4500 metres. The length of the glacier from the place where it merges into the Inland Ice is approximately 21 kilometres, A point where the side of the fjord disappears under the Inland Ice is more than 150 metres above the sea ; hence the slope of the glacier is not quite half a degree. The glacier passes evenly into the Inland Ice, which slopes slowly upwards beyond it.

The icebergs in front of the end of the glacier not seldom overtop it by as much as 30 metres, for its terminal ice-wall rises scarcely more than 40 metres from the sea. The line where the glacier ends and the bergs begin is in this case easily observed, for though its surface is much fissured, the outline of the bergs is even more con- fused ; but the end of the glacier is indicated still more clearly by a thin layer of fine dust, which distinguishes it from the cleaner sur- face of the recently broken-ofF and overturned bergs. The sides of the Jakobshavn Fjord are not very steep or high, and so it is not difficult to traverse its south side.

The usual method of measuring the rate of motion of a glacier, by fixing a line of poles across it, cannot be applied in the ice-fjords, by reason of the inaccessibility of the glacier ; it therefore has to be determined by the measurement of angles from a fixed base, the sharp peaks affording good points for observation. My measure- ments were made with a good theodolite, and the results are given in the following Table (p. 149).

The rate of motion, where the glacier borders upon the moun- tain-side, was measured by fixing sharp stones into the side of the glacier, and by laying on the rock close to the glacier similar sharp stones, so that the sharp points of the stones in the glacier were lying quite near the points of the stones on the rock. It was observed that the rate of motion close to the border of the glacier was not over 0*02 metre per day.

These numbers show that the Jakobshavn glacier flows with a velocity greater than any that has hitherto been observed *. This is the more surprising as its slope is only half a degree. The measure- ments were made daring the daytime in summer, when the tempe- rature rose at noon to 10° C. ; perhaps the motion is slower on colder days. There must, however, be considerable motion during

de Glace (Chamouni) was 33| inches (0-85 metre). This was in the month of June. See ' Glaciers of the Alps,' p. 280.— Ed.]
 * [The maximum daily motion as observed by Professor Tyndall on the Mer