Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/191

Rh AND CIRQUES IN NORWAY AND GREENLAND. 153

properly provided with European attendants, a ladder, ropes, &c., to traverse this part of the glacier ; but the unusually numerous crevasses would certainly make it difficult. Perhaps it would be more easy to pass over to Umiamako by the north side of Kangerd- lugssuak, though the steepness of the fjord side and the glaciers in the lateral glens would make the excursion toilsome.

The fact that though the climate of North Greenland, as already mentioned, is rather dry, large glaciers are numerous, is not with- out geological importance, as showing that a great snowfall is not absolutely necessary for the glaciation of an extensive country. It is also remarkable that the glaciers are supplied from an ice-field which, to a large extent at least, lies below the limit of perpetual snow. No doubt there is always a difficulty in determining this ; for ex- ample, in the district of Unianak one may find masses of snow in summer near the sea, as in the island of Upernivik, even in the middle of August ; but I ascended over the shales and sandstones * to a height of 750 feet above the sea without meeting with snow. At this elevation there is a plateau rising up to 890 metres, yet this is only dotted over with some patches of snow ; so that in this island the line of perpetual snow lies above 890 metres. In the mountains on the opposite side of Umanak Fjord, east of Kelerting- uak mountain, masses of perpetual snow are only found at heights above 700 metres. Above the glacier of Sermiarsut the limit was 970 metres, between the glaciers of Assakak and Umiatorfik 800 metres, and between the latter and the glacier of Sorkak 760 metres.

By comparing these numbers with the height of the Inland Ice where it has been measured, we see that the limit of perpetual snow on the outer land exceeds it : for example, at Pakitsok the Inland Ice was 251 metres above the sea, and Professor Nordenskjold reached an elevation of 690 metres ; but by looking at the bordering mountains one can see, without measurements, that the above statement is true. It is therefore doubtful if the ice-sheet and the glaciers would form again could the land be denuded of them and left to the influences of the present climate. The rate of flow, already mentioned, has an important bearing on the theory of glacier- motion. As the slope of the Jakobshavn glacier, which has the extra- ordinarily rapid motion of 20 metres per diem, is only half a degree, the fall of the bed of the valley cannot be the most important factor in the motion of glaciers. This considerable velocity must be due to the quantity of ice which has to be carried out to the fjord ; or, in other words, the rate of motion is dependent on the pressure of the mass of the Inland Ice. Glaciers, therefore, fed from large districts of atmospheric precipitation, move with considerable velocity. Notwithstanding the rate of flow, the time occupied by the passage of the ice from the interior to the sea must be long. At the Jakobshavn glacier, indeed, four years would be required to transport a mass from the edge of the Inland Ice to the sea, a distance of 21 kilometres ; but a much longer period would be required to transport to the sea the snow which falls on the interior
 * These contain coal and fossil plants.