*873-] Coral Reefs and the Glacial Period. 175 



There is another point which might perhaps throw some light 

 upon the question. It is well known that high equatorial 

 lands or corn lands south of the equator are tenanted by 

 north temperate forms of life, left on the mountain ranges in 

 such latitudes as the extreme cold of the glacial period 

 decreased. Darwin says,* "From the presence of temperate 

 forms on the highlands across the whole of equatorial 

 Africa, and along the peninsula of India to Ceylon and the 

 Malay Archipelago, and in a less well-marked manner across 

 the wide expanse of tropical . South America, it appears 

 almost certain that at some former period, no doubt during 

 the most severe part of the glacial period, the lowlands of 

 these great continents were everywhere tenanted under the 

 equator by a considerable number of temperate forms. At 

 this period the equatorial climate at the level of the sea 

 was probably about the same with that now experienced at 

 the height of from 5000 to 6000 feet under the same 

 latitudes, or perhaps even rather cooler. During this, the 

 coldest period, the lowlands under the equator must have 

 been clothed with a mingled tropical and temperate vegeta- 

 tation." 



Now if both hemispheres were simultaneously visited by 

 an extreme glacial period, we should expect to find about an 

 equal share of northern and southern forms left about the 

 equatorial highlands, unless, indeed, the ice-sheet was much 

 more developed in the one hemisphere than the other, which 

 might arise from larger areas of land on one side of the 

 equator than the other. At all events we should not expect 

 to find a very marked preponderance of forms from one side, 

 especially along those equatorial parts with continental 

 tracts of land both north and south. 



Again, if the extreme glacial climate has visited the 

 southern hemisphere at a later date than the northern, we 

 should expect to find a preponderance of south-temperate 

 forms of life on equatorial highlands rather than of north- 

 temperate forms, especially along those parts of the equatorial 

 belt where there was continental land to the south. Lastly, 

 if the glacial period prevailed in the northern hemisphere 

 some time after the last cold era in the southern, the north- 

 temperate forms of life would prevail on equatorial high- 

 lands almost to the exclusion of south-temperate — these 

 latter being the relics of a former southern cold. What do 

 we actually find to be the case as regards this distribution 

 of north- and south-temperate forms respectively ? I again 



* Origin of Species, p. 455. 



