166 DALY. 



Pleistocene Temperatures of the Tropical Ocean. 



In spite of conflict of views as to the cause of Pleistocene glaciation, 

 it is clear that it was accompanied by some fall of average air tempera- 

 ture and of average ocean temperature, in the northern hemisphere at 

 least. In that hemisphere the great ice-caps, then larger than the 

 present ice-caps by nearly 16,000,000 square kilometers in total area, 

 were not merely the result of an atmospheric condition very difi"erent 

 from that of the present time. The ice-caps in their turn must have 

 seriously affected the wind system and therefore the system of surface 

 currents in the sea. The annual shifts of the currents and changes in 

 the paths of great storms, characterized by extremes of air temperature, 

 must have often lowered the sea temperature below 20° C, even in 

 parts of the ocean where the mean annual temperature may have been 

 above 20° C. Though occurring but once a year, a few days' exposure 

 to a temperature below that point would seriously endanger the life 

 of the i-eef-building corals. 



The growing l)elief among glacialists, that the southern hemisphere 

 was locally glaciated at the same time as the northern hemisphere, is a 

 second principal reason for postulating a great restriction of coral 

 reefs in the Pleistocene. The glaciers of the Andes, from the equator 

 to Cape Horn, were much larger than now, at a time which is most 

 probably placed in this geological period. Of similar date are the 

 formerly expanded glaciers of Central Africa and New Zealand, and 

 the Antarctic ice-cap seems to ha^'e been much thicker and more 

 extensive during the Pleistocene. The notable glaciation of southern 

 regions now bearing no perennial ice, as New South Wales (35° S. 

 Lat.), Western Tasmania (42^ S. Lat.), Campbell Island (52.5° S. Lat.), 

 the Auckland islands (51° S. Lat.), Macquarie island (55° S. Lat.), 

 the Falkland islands (51° S. Lat.), and the eastern highlands of South 

 Africa (28° S. Lat.), has been recently referred to the same period. ^^ 



For the northern hemisphere special importance must be attached 



11 C. A. Siissmilch, An Introduction to the Geology of New South Wales, 

 Sydney, p. 152 (1911); W. H. Twelvetrees, Proc. Rov. Soc. Tasinania, p. 72, 

 (1900); J. W. Gregory, Quart. Jour. Geol. Soc, 60, 37 (1906); E. J. Dunn, 

 Proc. Roy. Soc. Victoria, 6, 133 (1894); P. Marshall, The Subantarctic Islands 

 of New Zealand, Wellington, p. 689 (1909) ; R. Speight, ibid., p. 705; D. Maw- 

 son, The Home of the Blizzard, Philadelphia and London, 2, 292 (1914), and 

 personal communication; A. Supan, Grundziige der phvsischen Erdkunde, 

 3rd ed., Leipzig, Plate XIII (1903). Compare T. W. E. David, Comptes 

 rendus, Cong. geol. internat., Mexico (reprint, 1907), pp. 31-38 (1906). 



