NARRATIVE OF THE CRUISE. 
969 
deeper waters of which it very materially contributes. Another equally remarkable 
current is that which brings the cold water from the south polar regions up along the 
South American coast at the bottom as far as the Equator. The bottom water in the 
corresponding situations in the Pacific and Indian Oceans is found to be much warmer j and 
it is probable from this fact that the depth between. Cape Horn and the south polar 
land is much shallower than that between either Africa or Australia and the same land. 
In any case it is certain that facilities must exist here for promoting the flow of cold 
water at the bottom from high Antarctic latitudes into the lower latitudes of the South 
Atlantic Ocean. The South American continent extends to the parallel of 56° S. The 
depth of the sea to the south is unknown, but from the edge of the bank south of the 
Falkland Islands to the South Shetland Islands is only 380 miles, so that there is some 
reason in dealing with water at depths of 1500 fatho m s and upwards, for assuming a 
direct connection between the American continent and these islands. Farther to the 
eastward there are three groups of islands, namely, South Orkneys in 61° S., the Sand- 
wich group in lat. 59° to 56° S., and South Georgia in 54° S. All of these are covered 
with eternal snow, and are exposed to a glacial climate. Of Georgia, which lies 2° farther 
north than Cape Horn, the bays are terminated by ice cliffs of considerable height, 
and according to Cook the country in the very height of summer is in a. manner wholly 
covered many fathoms deep with frozen snow, but more especially on the southwest 
coast. 1 In the ice chart of the Southern Ocean the line “ freezing point in air in 
January and February” passes through the Sandwich and South Shetland groups, and the 
northern limit of icebergs reaches the very low latitude of 40° S. The dense water of 
the tropics, which has been diverted in 1 a southerly direction by the South American 
continent, is brought directly into this very cold climate, and by virtue of its great 
salinity affords the means of promptly conveying the surface cold to the bottom. If this 
cold water have a tendency to flow from the poles, it will in these high latitudes experience 
a strong thrust towards the westward, due to the increasing rotational velocity of the 
earth’s surface. That this does take place is shown by the low bottom temperatures 
observed at every Station along the western side of the South Atlantic almost to the 
Equator, and that there is here a sensible current of cold water along the bottom is 
shown by the sudden change in the rate of decrease of temperature with increasiug depth 
which is observed at depths of from 2000 to 2200 fathoms. It shows that the water 
between the bottom and 2000 fathoms is nearly as distinct from the water above it as the 
water of the “ cold wall ” on the North American coast is from the Gulf Stream outside 
it. The temperature observations on the 28th and 29th February 1876 show that the 
surface of this cold stratum is not level, but rises towards the American shores. On the 
28th February the Station (323) was in lat. 35° 39' S., long. 50° 47' W., depth 1900 
fathoms, and therefore on the continental declivity forming the western containing 
1 See Darwin, Journal of Researches during the Voyage of H.M.S, “Beagle,” p. 248, ed. 1879, 
