Geological Aspects of the Coral-Reef Problem. 207 



Some consideration was devoted to the solvents which play an 

 •essential part in metamorphism and to the limits of migration of 

 dissolved material within a rock-mass. The Address proceeded to 

 the discussion of what is the most fundamental characteristic of 

 metamorphism : namely, that recrvstallization takes place in a solid 

 environment, and so may be profoundly affected by the existence 

 of shearing stress Stress of this type, on the one hand, arises from 

 the crystal growth itself, and on the other hand is called into play 

 by external forces. The automatic adjustment of the internally 

 created stress to neutralize that provoked from without affords the 

 key to all structures of the nature of foliation. The mineraWical 

 peculiarities characteristic of the crystalline schists must find 

 their explanation in kindred considerations ; for it can be shown 

 that the chemistry of bodies under shearing stress differs in im- 

 portant respects from the chemistiy of unstressed bodies The 

 result is seen m the appearance of a certain class of < stress- 

 minerals where the dynamic element has figured largely in 

 metamorphism, while in the same circumstances the formation 

 ■or minerals of another class seems to have been inhibited. But 

 while some of the general principles governing the effects can be 

 formulated, the explanation on these lines of the observed asso- 

 ciations of minerals is a task for the future. It may be that 

 many of the particular problems involved will in time be brought 

 within the scope of laboratory experiment. 



The conditions governing metamorphism are temperature and 

 shearing stress with uniform pressure as a factor of less general 

 importance If the erogenic forces are sufficient to maintain 

 shearing stress everywhere at its maximum, the stress itself 

 becomes a function of temperature, since this determines the 

 elastic limit, and the principal conditions of metamorphism come 

 to depend upon a single variable. This degree of simplification, 

 however, is not to be expected universally. One disturbing factor 

 is the local rise of temperature sometimes caused by the mechanical 

 generation of heat in the crushing of rock-masses. 



February 20th.— Mr. G-, W. Lamplugh, F.B.S., President, 

 in the Chair. 



The following communication was read : 



'The Geological Aspects of the Coral-Beef Problem.' By Prof 

 William Moms Davis, For.Corr.G-.S. 



th a T A e a C0 T Unieat . i0 / iS \ cHtical review of the ™*» theories 



oril of on 66 '? PU f f °T ai ' d UP t0 the P resent time t0 «P lai « the 

 1QM. h f:l ■«*••*■ ™y»ge in the Pacific, made in the vear 

 1914 enabled the author to collect new evidence bearing upon the 



ttfissssr^***- influence dliJ ' in Ms 



of ^t r v! aymg J? 8 " T" the emba 3™entof shore-lines as a proof 

 of subsidence, the author expresses the opinion that all theories 



