GLACIAL-CONTROL THEORY OF CORAL REEFS. 167 



to the proofs that glaciers, doubtless Pleistocene in date, existed in, 

 or close to, the coral-reef areas of the ocean. Among the more telling 

 instances are those in Hawaii, Japan, Mexico, and East Africa. 



Locating all these lands on a world map, the reader will note how 

 inevitable is the conclusion that the tropical seas were considerably 

 cooler during the Pleistocene. Philippi finds further evidence of that 

 fact in the character of the deep-sea ooze collected in the Indian ocean 

 (between 0° and 55° S. Lat.) by the "Gauss" expedition. He shows 

 that the content of calcium carbonate in this deposit decreases with 

 increasing depth and he attributes this decrease to special chemical 

 conditions due to Pleistocene chilling. -"^^ 



Much more difficult is the question as to the actual amount of 

 Pleistocene chilling of the tropical seas. The lowering of snow-line at 

 that time was at least 900-1,000 meters in Hawaii and Japan, ^^ about 

 1,500 m. in equatorial America, and at least 2,000 m. in equatorial 

 East Africa. With those estimates the Pleistocene lowering of snow- 

 line 1,000 to 1,500 m. for Central Europe, about 2,000 m. for southern 

 British Columbia, and nearly 2,000 meters for the northeastern United 

 States, may be compared. 



In the lowlands of Java the Selenka expedition found the remains 

 of Pleistocene species of plants wliich now grow in that island at 

 levels from GOO to 1200 m. higher. ^^ 



The average decrease of air temperature with increase of altitude 

 in mountainous districts, for the first 5,000 m. above sea, is al)out 

 0.56° C. per 100 m. The a^'erage decrease determined only from 

 summit stations is nearly 0.65° per 100 m,, which is close to the gradient 

 for free air. These mean values for the decrease practically apply 

 both to the temperate and tropical zones. ^^ 



Since the relative precipitation, the relative effect of insolation, and 

 other factors of Pleistocene climates are not determined, the beha\ior 

 of the Pleistocene snow-line cannot, in general, give a direct value 

 for the average lowering of air temperature within the tropics at that 

 time. The best estimates are doubtless those to be derivefl from lands 

 exposed, then as now, to an oceanic climate; for example, Auckland 

 island, New Zealand, Hawaii, Vancouver island, the Coast Ranse of 



12 E. PhiUppi, Zeit. deut. geol. Ges., 60, 354 (1908). 



13 H. Simotomai, Zeit. Ges. Erdkunde, BerUn, No. 1, p. 56 (1914). 



14 A. Tornquist, Grundziige der Formations- und Gebirgskunde, Berlin, p. 

 279 (1913). 



15 J. Hann, Handbook of Climatologv, trans, bv R. DeC. Ward, Xow York, 

 Part I, p. 244 (1903). 



