812 
MR J. M. WORDIE ON THE NATURAL HISTORY OF PACK-ICE 
means of one of these lanes, the ship moved to a new position 400 yards away, and 
was secured in a narrow lead not much more than the width of her beam. All 
would have been well had she not been warped round into a transverse crack four 
days later, for this move left her at the meeting-point of three floes. When pressure 
began again, instead of rising with it, she was twisted by the working of the three 
floes and developed a bad leak at the stern-post on October 24. No longer 
buoyant, she was now unable to weather such pressures as formerly would have 
given little trouble, and finally on October 27 she was abandoned, the bottom torn 
out of her and the water flush with the upper deck. She remained thus for a month, 
and it was not till November 21 that' she finally sank under water. 
A word may be said about height of pressure ridges , since there has always been 
a tendency to exaggerate this feature. During these fifteen months in the Weddell 
Sea it was quite exceptional for any ridges to be as much as 15 to 20 feet high ; those 
of July and August 1915 were only 12 to 14 feet in height. On one occasion about 
three miles from the ship a hummock was found 25 to 30 feet high, built up entirely 
of blocks of sea-ice ; it was not, however, part of a pressure ridge, but was simply an 
isolated hummock due probably to the encounter of two jutting corners. Again in 
March 1916, a thick slab of sea-ice was tilted up so that the upper edge was 25 feet 
above water-level ; in this case at any rate it certainly was a jutting floe corner 
which had had to give way during screwing movement. 
Accounts from the North have given the impression of extremely high pressure 
ridges in the Arctic seas. All these accounts, where reliable, are found to be based 
on phenomena seen north of Baffin Bay and Kobeson Channel, where the land 
offers considerable obstruction to the drifting ice, and possibly causes higher ridges 
than on the open sea. Nansen, on the contrary, definitely states that on the drift 
of the Fram across the North Polar Basin itself the highest hummock was 30 feet, 
and comparatively few exceeded 20 feet. 
Should pressure ice, therefore, be met with in the South whose average is above 
20 feet or even above 15 feet, it must point to the existence of land obstructing the 
free drift of the ice. A case in point was the belt of heavy hummocky -ice found by 
the Endurance on her southward voyage stretching from 70° S. 15° W. to 71° S. 
22° W. ; the floes were so close and heavy that it took six days to find a passage 
through. This very heavy ice was regarded as pointing to a deep embayment some- 
where east of Coats Land, or at least to a very large ice-tongue protruding from the 
coast and so checking the westerly drift. 
Pressure ridges were highest and most prominent when newly formed. They 
almost immediately sank to a position of equilibrium, as required by the specific 
gravity of the ice, the ratio of ice below to that above water being either 4 to 1 or 
5 to 1. Possibly, as Weyprecht suggests, the supporting floes and pieces, which at 
least in the upper two-thirds were dry before the hummocking, when driven below 
became waterlogged and so lost some of their buoyancy. Whatever the cause, the 
