46 PROCEEDINGS OP THE WASHINGTON MEETING 



CORAL-REEF PROBLEM 

 BY W. M. DAVIS 



(Abstract) 



The author, having reviewed various coral-reef theories preparatory to his 

 Shaler Memorial voyage of 1914, and having visited on that voyage thirty-five 

 reef-encircled islands in the Pacific, is now preparing a report on his observa- 

 tions and inferences. He finds in this connection only three theories that 

 demand serious consideration — Darwin's theory of subsidence, Daly's theory 

 of glacial control, and Vaughan's theory of submerged platforms. The present 

 paper sets forth the difficulties that stand in the way of accepting two of these 

 theories. The theory of glacial control seems inadequate because it excludes 

 subsidence on insufficient grounds, because it assumes unwarranted conditions 

 for preglacial islands, and because certain essential consequences of its main 

 process — the truncation of low preglacial islands by the lowered and chilled 

 ocean of the Glacial period- — are not found on Pacific islands. The theory of 

 submerged platforms is unsatisfactory because it assumes without sufficient 

 warrant the origin of the platforms independent of coral agencies, because it 

 assumes the absence of reef-building corals during the production of the plat- 

 forms, because it provides no adequate cause for the production of flat plat- 

 forms in close association with steep volcanic islands, and because it excludes 

 all but small changes of level in reef-encircled islands during recent geological 

 periods. 



Presented in abstract extemporaneously. 



Eemarks were made by Professors R. A. Daly and J. P. Iddings, with 

 reply by the author. 



TERTIARY -QUATERNARY OROGENIC HISTORY OF THE SIERRA NEVADA IN 

 THE LIGHT OF REGENT STUDIES IN THE YOSEMITE REGION i 



BY F. E. MATTHES 



(Abstract) 



It is a noteworthy fact that the hanging tributaries of the Merced are not 

 all graded with respect to the same former profile of the master stream. 

 Those flowing over the massive and resistant granites of the Yosemite region 

 indicate an old profile situated about 2,800 feet above the present canyon floor. 

 Those flowing over normally jointed and relatively easily eroded rocks indicate 

 a more strongly concave profile of a later date, situated 600 to 1,200 feet lower. 

 The older profile of the Merced appears to be coordinate with the profiles 

 determined by Lindgren for the Tertiary rivers of the northern Sierra Nevada 

 (by means of the auriferous gravels). The younger profile of the Merced is 

 believed to correspond to that stage of erosion which Lawson has recognized 

 in the Chagoopa Plateau of the Kern River country. It clearly antedates the 

 cutting of the inner gorge of the Merced, just as the mature valleys of the 

 Chagoopa Plateau antedate the cutting of the Kern's narrow canyon. Inner 



1 Published with permission of the Director of the U. S. Geological Survey. 



