ADVISORY COMMITTEE ON GEOPHYSICS 3 1 



Some of the salient problems of the outer litliosphere are the ori- 

 gin and maintenance of the continental platforms — with their super- 

 posed mountains and plateaus — and the abyssmal basins, involving 

 questions of rigidit}^ isostasy, etc. ; the agencies and conditions 

 that make possible the prolonged periods of crustal quiescence 

 shown in baseleveling, and the antithetical epochs of crustal dis- 

 turbance ; the sources of crustal displacement and distortion, shown 

 intensely in the faulting and in the crumpling of mountains and 

 plateaus, and shown massively in the continents and oceanic basins ; 

 the mashing, shearing, and foliation of the rocks leading on to the 

 general problems of metaraorphism, and a whole group of intricate 

 questions of a chemical and chemico-physical nature, including the 

 flow of rocks, the destruction and genesis of minerals, the functions 

 of included water and gases, the internal transfer of material, the 

 origin of ore deposits, the evolution and absorption of heat, and 

 other phenomena that involve the effects of temperature, pressure, 

 tension, and resultant distortion upon chemical changes and minera- 

 logical aggregations. 



These questions of the earth's outer part are inseparably bound 

 up with those of the interior, and here the problems involve the 

 most extreme and the least known conditions, and make their 

 strongest demand for experimental light. The themes here are the 

 kinds and distribution of the lithic and metallic materials in the 

 deep interior : the states of the matter ; the distribution of mass and 

 of density, and the consequent distribution of pressure ; the origin 

 and distribution of heat ; the conductivities of the interior material 

 under the pressure and heat to which it is subjected ; the heat possi- 

 bilities arising from supposed original gaseous condensation , or al- 

 ternately from initial impact of aggregation ; the heat of subsequent 

 attractional condensation ; the secular redistribution of heat within 

 the earth , and its loss from the surface ; the possible relations of 

 redistribution of internal heat to vulcanism and to deformation, and 

 similar profound problems. 



A series of specific laboratory questions arise from these, e. g., 

 the effect of pressure on the melting point of rocks carried to as 

 high temperatures and pressiu'es, and through as wide ranges of 

 material as possible, to develop the laws of constancy or of varia- 

 tion ; the effect of temperature and pressure on thermal conduc- 

 tivity as indicated above, and on elasticity, especially as involved 

 in the transmission of seismic tremors. 



