292 DEACON [CHAP. 12 



way : as the line to the north of which we felt one day, at the right season, 

 after months in the Antarctic, genial air again and soft rain like English rain 

 in the spring. I can remember a number of those days vividly. It was like 

 passing at one step from winter into spring. In the southernmost lands in the 

 sub-Antarctic, the islands about Cape Horn, the earth smells as earth should 

 smell and as it never does in the Antarctic. It is, no doubt, the north-easterly 

 course of the convergence between the longitudes of Cape Horn and South 

 Georgia, so that the former is left far to the north and the latter to the south, 

 that accounts for the vast difference in the climate of two islands which are in 

 precisely the same latitude and only 1000 miles apart. The lower slopes of 

 Staten Island are clothed with beech trees with so rich an undergrowth that it 

 is difficult to push through. Darwin compared the richness of the region to that 

 of a tropical forest. South Georgia, the other island, is a true Antarctic land. 

 The snow-line of South Georgia is lower than the tree-line of Tierra del Fuego." 



Many of the zoologists who have examined the Discovery collections have 

 remarked on the significance of the convergence as a biological boundary. 

 Among the floating and drifting plants and animals there are many species 

 which are typical of either Antarctic or sub-Antarctic water, and sufficiently 

 rare on the other side of the convergence to be regarded as intruders if found 

 there. Others are common to both sides. Among the free-swimming animals the 

 coastal fishes were shown by Tate-Regan (1914) to be best divided into Ant- 

 arctic and sub-Antarctic species by the 6°C isotherm, which follows the Antarctic 

 convergence very closely, and Norman (1938), using all the new material, based 

 his classification on the position of the convergence, the result being almost 

 the same. An example of its significance for bottom-living animals is afforded 

 by the non-abyssal Polyzoa for whose distribution Hastings (1943) found the 

 division into Antarctic and sub -Antarctic species to be the most conspicuous 

 feature. The great majority were found in one region or the other but not in 

 both. Murphy in his book on the oceanic birds of South America (1936) gives 

 a list of fifteen birds typical of the Antarctic zone, twenty-nine of the sub- 

 Antarctic zone and eleven common to both. 



There is some interrelation between the position of the convergence and the 

 boundaries of different marine sediments at the bottom of the ocean, and 

 evidence provided by the stratification of sediments in certain areas has been 

 used by W. Schott (1939) to demonstrate the probably greater extent of the 

 Antarctic zone during the Glacial Period. Round the Antarctic continent there 

 is a wide belt of glacial mud, but the proportion of this deposit decreases to- 

 wards the north, and in the northern part of the Antarctic zone, where the 

 growth of diatoms is particularly abundant, the sediment consists mainly of 

 the siliceous skeletons of diatoms. Farther north, in the sub-Antarctic and 

 subtropical regions, the most typical sediment is calcareous, mainly Globigerina 

 ooze composed chiefly of the skeletons of pelagic Foraminifera. The chief excep- 

 tions are deep-water areas of red clay occurring where the calcareous material 

 has been dissolved, and Wiist (1934) has shown that the extent of these areas is 

 closely correlated with the northward movement of the Antarctic bottom 



