GEOPHYSICAI, INVESTIGATIONS SUGGESTED 199, 



6. The relation between the size of crystals and — 



(fl!) The composition of the mineral liquid — the sol- 

 vent. 



(J)) The rate of cooling. 



(c) The mobility of the molten magma, and its con-^ 

 tent of gas. 



(^) The pressure. 



7. The relation between the habit (shape) of crystals and- 



(a) The composition of the mother liquor. 



(^) The 7'ate of growth. 



(^) The molecular mobility of the mother liquor. 



{d^ The absence or presence of currents or motion 



at the time of crystallization. 

 ((?) The pressure. 



8. The textnre of rocks in its relation to — 



(a) The development of phenocrysts by partial crys- 

 tallization of the magma at one rate and the 

 solidification of the remainder at another rate 

 (to be effected by change of physical environ- 

 ment, change of temperature, or pressure). 



{b) The diverse rates of growth of diverse minerals, 

 in mixed solutions. 



{c) Synchronous intergrowths of mixed salts, as of 

 quartz and orthoclase. 



{d) The effect of localized ' ' crystallizers ' ' in pro- 

 ducing centers of crystallization resulting in 

 spherulites, segregations, etc. 



((?) The possible development of " protoclastic " 

 texture in moving crystallizing magma. 



The physical investigations should be accompanied by close chem- 

 ical studies. The precise chemical composition of all material ex- 

 perimented on should be determined. 



The role played by certain elements in minerals should be investi- 

 gated, such as the possibility of Al^Oj behaving as an acid radical in 

 the feldspars, etc. 



The molecular constitution of the more complex silicates may be 

 investigated by means of the determination of the specific heat ol 

 the minerals. 



