P. A. Daly — Problems of the Pacific Islands. 185 



reef-making ? Are these other species affected by relatively 

 small changes in temperature ? 



5. Direct observations are needed to test the scope of mud- 

 control, which seems to explain so well the position and shape 

 of each atoll and barrier reef. 



6. The Glacial-control theory demands that the oceanic 

 islands should generally have rimming platforms at average 

 depths of about 200 feet, except in the case of those islands 

 that have undergone uplift or subsidence since the Glacial- 

 period. Recent vertical movements are recorded for 72 islands. 



Figs. 34-38. 



W. 39 38 37 34 34 35 29 24 28 15 FR 



FR 19 24 38 40 35 E. 



S.W. 80 50 49 55 53 52 52 30 53_47_44 34 14 



20 19 18 12 10 8 6 



||l||!!|l|||||l|llimi|ii!Mimi||miiilll 



36 



llill 



^ 



Figs. 34-38. Sections illustrating a fringing reef, uplifted islands, and a 

 barrier reef. Water is shown in solid black ; rocks are lined. Uniform 

 scales ; vertical scale is seven times the horizontal. Depths in fathoms. 



34. Rodriguez island, Indian ocean, with a typical fringing reef (FR) and 

 a broad, reefless platform offshore. This island appears not to have been 

 affected by crustal movement in the Recent period. 



35. Vavau cluster, Tonga group, an uplifted (probably tilted) limestone 

 plateau, which has been greatly eroded. Note depth of platform on the 

 southwest. 



36. Uvea, a tilted atoll of the Loyalty group. The varying depth of the 

 lagoon is a function of the differential uplift. 



37. Christmas island, Indian ocean, a strongly uplifted composite of Ter- 

 tiary limestone and volcanic rocks. Note the absence of a submarine bench. 



38. Mbengha island, Fiji group, a typical barrier reef, little or not at all 

 disturbed by Recent crustal movement. 



Forty-one of those uplifted have been charted in detail sufficient 

 to allow a test of the new theory. All forty-one either lack 

 submarine shelves entirely or have platforms at levels situated 

 as far above that of minus 200 feet as would correspond to the 

 respective amounts of uplift. Figure 37 is a section of Christ- 

 mas island in the Indian ocean, an important source of guano. 

 Uvea, of the Loyalty group, is a tilted atoll, as indicated in fig. 



Am. Jour. Sci. — Fourth Series, Vol. XLI, No. 242. — February, 191(1. 

 13 



