PIEDMONTS- AFLOAT. 
67 
as that of Coulman Island are sometimes as much as 15 miles long, but are 
rarely more than 2 miles broad. The snow encircles the rock-cliff up to heights 
of 200 to 400 feet above sea-level, and the seaward edge is not often more than 
70 feet above water. The distinction between “ piedmont-on -land,” and “piedmont- 
aground” is to some extent hypothetical, for it is difficult to make sure that ice 
at any particular point does not extend below sea-level (Fig. 56, p. 93). 
On Sturge Island of the Balleny Group, a transition from “ piedmonts- 
aground ” to “ piedmonts-afloat ” is also evident, for sometimes the undulating fringes 
flatten out along definite lines parallel to the shore and extend at least 5 miles out 
to sea, and so are probably partly afloat (Fig. 1, p. 3). 
(c.) Pied monts-ajloat. 
Piedmonts-afloat are represented by four important examples,' (l) the sheet of 
ice which fills up Lady Newnes Bay, (2) the sheet at the foot of Mount Neumayer, 
Drygalski Piedmont, (3) the sheet which extends from Cape Gauss eastwards for 
20 miles at least, Nordenskiold Piedmont, and (4) the Ross Ice-sheet, or Great 
Ice Bai’rier of Ross. All these are characterised by great extent with flat or slightly 
undulating surface, and by a clitf-edge between 50 and 200 feet high, which has 
enough water immediately in front of it to completely float the ice. The best 
known of these floating piedmonts is the ice-mass which Ross in 1841 called the 
Great Ice Barrier, but as this name entirely fails to convey the idea of vast extent, 
we conclude not to adopt it as a general type, but prefer rather to class the Ice 
Barrier of Ross and similar ice-masses as a subdivision of Russell’s term ‘ Piedmont.’ * 
The Ross Piedmont has a seaward edge some 500 miles long, and its terminal edge 
rises to an average height of 150 feet (Fig. 38). The depth of water close to this 
ice-face is usually between 300 and 400 fathoms, and the sea-floor is covered with 
fine rock-flour. If reference be made to the chart at the end of the volume, 
details of heights and depths along it may readily be seen. If it be assumed 
that aerated glacier-ice floats with at most six-sevenths of its volume immersed 
in sea-water, f we may take it that the height in feet of the sea-cliff above is 
equivalent to the depths in fathoms below, and hence that this ice-cliff must 
be afloat. Further evidence that it floats is afforded by the tide-crack around 
Mount Terror, White Island, and in many other places. The uniform horizontality 
of the upper surface was proved by Captain Scott in his sledge- journey to 
the south, and by Lieutenant Royds and Mr. Bernacchi in their trip for 155 
miles to the south-east. 
The intimate structure of Piedmont-ice shows that as far as water-level it consists 
of normal glacier-ice. On the surface away from the land only fine snow was met 
* I. C. Russell, ‘ Glaciers of North America,’ 1897, pp. 2 and 3. 
t Heim, ‘ Handbuch der Gletscherkunde,’ 1885, p. 278, and H. Rink, 1 Danish Greenland,’ 1877, p. 358. 
K 2 
