The observations made with regard to this subject confirm what was already known from the examination of the arctic ice. The ice directly produced by the freezing of sea-water is never of great thickness, but this thickness increases on one side by the accumulation of snows on its surface, and on the other by the heaping of blocks during the pressure. These mechanical phenomena are able to form slabs eight metres in height. The pressures are produced, in the regions explored by the Belgica, by the wind, which is thus foretold: In summer, during calm weather, there is always a change in the ice-pack, which is accompanied by a formation of cracks and leads. The pressure is produced afterwards, but before the wind is felt; it generally ceases some time after the wind prevails and when the ice-pack is drifting. This seems to me to prove that the pressure is the result of difference in the velocity of the drifting parts of the ice-pack, and this difference is due to the fact that a wind which begins to blow drives the portion of the ice-pack on which it blows upon the rest, which has not hitherto felt its influence.
It must be said that the pressure may also be produced when the ice-pack is driven by the wind against land. The icebergs met by the expedition are incontestably formed by an ice which has a different origin from that which forms the ice-pack, properly speaking. An iceberg is indisputably a fragment of a terrestrial glacier. All the particulars which we have been able to state, concerning the structure of the floating iceberg, were equally observed in the structure of the façades of the glaciers of Belgica Strait.
OCEANOGRAPHY
A sounding-line was much used between Staten Island and the South Shetlands. It allowed us to find out that Drake Strait is the prolongation of the oceanic basin of the Pacific. At a short distance from Staten Island the continental plateau falls abruptly from 296 metres to 1574 metres; farther south we find 4040 metres; then the bottom rises gently towards the South Shetlands, which rest themselves upon a continental plateau. These soundings bring forth an important argument for those who, like myself, believe in the independence of the American and antarctic continents. The chain of the Andes, first directed from north to south, bends or inclines towards the east to Tierra del Fuego, and takes a west-easterly direction in Staten Island. Perhaps also this curve is in the direction of the north-east through the Falkland Islands. In the same manner the chains of Grahamland are divided from south-west to north-east, and through the South Shetlands from west to east, a direction which, in the South Orkney Isles, leans slightly towards the south-east. It seems to me that there is here a system of divergent chains. Other people, however, connect these two chains by means of a vast hypothetical curve. It is evident that this question can only be solved by the oceanographical study of the region comprised between New Georgia of the south and Drake Strait.
In Drake Strait the temperature of the superficial sheet of water is above 0°, but below its surface the temperature descends to -1°, to ascend again from 200 metres thereabout, and maintains itself in the depths above 0°, at the bottom (3660 metres), where it is +0.6°; the whole column of water cools progressively towards the south. The sheet of cold water signalled below its surface has the shape of a wedge, whose point is directed north and whose base is south. This sheet of cold water increases in thickness towards the south, and nears the surface at the same time. It is due to the presence and melting of icebergs.
In the region situated between longitudes 75° and 103° west, and from latitude 69° to latitude 71° 30′ south, the temperature of the water is somewhat diverse.
Above the continental plateau the superficial sheet of water has a temperature of -2°, but the temperature ascends gradually as far as the bottom, where it maintains itself between 0° and +1°. The cold water occupies a greater thickness than the warm water, and this thickness increases towards the south. North of the continental plateau the temperatures of the water are nearly the same as in Drake Strait. No constant currents were observed, although the ice-pack in which the Belgica was inclosed was in constant motion; and though the drifting movement exceeded sometimes ten miles a day, it is not possible to establish to a certainty the existence of a current. The drifting was certainly determined by the exclusive influence of the wind, and I do not doubt but that a careful comparison of the successive positions of the ice-pack and mariners’ cards will demonstrate it in a definite manner.
The sediments found upon the continental plateau and north of it are of a terreous origin, as stated before; but what is most remarkable is the great number of globigerinæ which are met there, and an absence of diatomaceæ. Yet the rapid examination of the plant showed a very abundant or rich flora of diatomaceæ, and almost no globigerinæ.
ZOOLOGY AND BOTANY
As I have already remarked, the Belgica Channel lands are entirely covered with a continuous and thick cloak of ice; a few small islands, shores, and perpendicular cliffs alone show the naked rock. Upon this limited portion of antarctic land can vegetation alone develop itself; and, indeed, it does on these spots. The only floriferous plant we found is of the order Gramineæ, which probably belongs to the Aira species; but the mosses (known among others, Barbula and Bryum) and the lichens (known among others, Lecanora, Verrucaria, and Usnea) are more abundant. On the spots where the water oozes from the melting snows there grow some soft water-wracks—oscillariaceæ and diatomaceæ.