Differentiation in Silicate Liquids. 191 



of tridymite were quite readily obtained in various mixtures of 

 the system: diopside, forsterite, silica. 



With the rate of sinking of the crystals as a basis rough 

 estimates were made of the viscosity of the melts, and they 

 show, as might be anticipated, a progressive increase of viscosity 

 with increase of silica. 



The importance is discussed of the sinking of olivine crystals 

 in the Palisade diabase sill to which J. V. Lewis has called 

 attention. Contact chilling may, by restriction of the process 

 of sinking of crystals, bring about the formation of a basic 

 contact phase. 



The fact is pointed out that the sinking of crystals cannot 

 safely be considered negligible even in acid magmas when they 

 occur in large bodies. 



Geophysical Laboratory, 



Carnegie Institution of Washington, 

 Washington, D. C. 



