AS OBSERVED IN THE WEDDELL SEA. 
805 
to be a case of fast-ice, and may possibly be a type of what Drygalski calls 
“ Schelfeis.” Whatever the naming of this ice may be (it is best called “ fast-ice ” 
when anchored, “land-floes” or simply “heavy pack” when adrift), emphasis must 
be laid on its occurrence being merely a temporary interruption of the normal 
sea-ice cycle. Should such an interruption, however, persist so as to verge on 
permanency, then an important new feature is produced, namely a barrier (or, as 
Nordenskjold and others now call it, “ shelf-ice ”). Direct freezing from sea-water 
ceases, but the ice-mass continues to grow by the addition above of successive 
layers of snow, which in due course become neve. When the Weddell Sea becomes 
fully known, several barriers will probably appear on the map. Here reference 
need only be made to the one found by Nordenskjold in the north-east portion 
of the sea, namely along the Oscar Coast of Graham Land. In his own descriptions 
it is referred to as a “ low ice-terrace ” ; but its height (30 metres) and the origin 
which he adopts for it make it quite comparable with the Great Boss Barrier ; and 
it has therefore been proposed to call it in future the Nordenskjold Barrier. 
Where the ice is not in motion, therefore, fast-ice is developed, and, in extreme 
cases, barriers or shelf-ice. These are the exceptions ; the rule is for sea-ice to be 
continually drifting. Bound up with the drift are the two related phenomena of 
cracks and pressure. 
Formation of Cracks. — Cracks were partly the effect of the ice being in motion, 
but they were much more often the immediate factor allowing movement. There 
was always a tendency (which will be explained later) for an ice-field, whether 
of young-ice or of hummocky-pack, to have cracks formed across it. The smaller 
areas so formed then shifted their relative positions under the driving influence of the 
wind. Then either wide leads and lanes were formed, or, on the other hand, ice- 
rafting or even heavy pressure resulted. So it comes about that, although the 
formation of cracks gives rise to leads and lanes and therefore makes the pack 
navigable, yet these very openings may themselves enable pressure and hummocking 
to begin, with consequent danger and difficulty to a ship attempting the pack. 
All cracks were a relief from strain, but the ultimate causes of the strain were 
very different, and in some cases unknown. In the Weddell Sea it was convenient 
to group the stresses as : — 
(i) Sudden differences of temperature — contraction cracks. 
(ii) Unequal loading — stress or strain cracks. 
(iii) Pressure. 
The treatment of cracks of the last category will be deferred till pressure comes 
to be considered. Elsewhere in the Antarctic and in the Arctic similar types of 
crack appear to be the rule. 
(i) Owing to the heavy autumnal snowfalls experienced by the Endurance in 
1915, the underlying ice was almost everywhere protected from the effects of 
