164 DALY. 



the Pleistocene ice-caps, and that the ice attracted the remaining sea 

 water, he wrote: " Such a rise of the sea, increasing in amount at high 

 latitudes, is attested b}' the modified drift of both America and Europe; 

 and coral islands afford proof of the corresponding depression of the 

 ocean, succeeded by a gradual elevation to its present height, over large 

 areas within the tropics. The coral islands of the tropics are witnesses 

 of a depression of the sea, amounting to 3,000 feet or perhaps much 

 more at the equator, while different proof shows that at the mouths of 

 the Mississippi, Ganges, and Po rivers it was at least 400 feet. If we 

 reflect upon the widespread changes of sea-level that marked the 

 glacial period, occurring only where they would be produced by taking 

 water from the sea to form the ice-sheets, and by gravitation through 

 their influence, and if we compare these recent simultaneous changes 

 with the general stability of the continents, it seems reasonable to 

 attribute them to movements of the sea rather than of the land." ^ 



Apparently without knowledge of the writings of Belt and Upham, 

 Penck threw out his suggestion in the following form (translated) : 

 " The causes of the general rise of sea-level in the latest geological time 

 might perhaps be connected with these climatic changes which the 

 earth underwent in the Glacial period. If, during that time, northern 

 Europe, northern North America, and the Antarctic regions were 

 simultaneously glaciated, a considerable mass of water must have 

 been removed from the ocean, and, if the thickness of the ice be 

 assumed as 1,000 meters, the sea-level must have been 150 meters 

 below its present position. However, it is conceivable that, in conse- 

 quence of the considerable cooling, the sea bottom sank during the 

 Glacial period, and since rose again, so that the size of the ocean basins 

 as a whole was not lessened. Whatever explanation is shown in the 

 future to be correct, it cannot be doubted that with a lowering of the 

 sea-level the zone of reef -building must also sink; hence that banks, 

 on which the corals formerly could not live, then became accessible 

 to those animals and could be built up into atolls. Further, with a 

 general lowering of the sea, many banks must become subject to wave 

 abrasion, which truncated them unless they were protected by growing 

 reefs. Thus the lowering of sea-level in the coral-reef region led to the 

 transformation of banks into islands and elsewhere to a further cutting- 

 away of the banks. In this way the fact is explained that the great 

 majority of the oceanic islands are found in the coral-reef region, while 



8 W. Upham, Geology of New Hampshire, Concord, 3, Part 3, p. 18 and 

 329 (1878). 



