BY H. I. JENSEN. 527 



deep sea deposits, and this has to be reduced and added to the 

 average composition of the sedimentary rocks. 



The sedimentary rocks analysed having been in most cases 

 slates and schists examined for a special purpose, are in most 

 cases of shallow water origin and naturally rich in potash carried 

 to the sea as mud, or precipitated from solution in glauconite, 

 phillipsite, harmotome, or other zeolites. 



Professor Sollas, in his work on "The Age of the Earth," has 

 given space to Joly's theory, and has raised other arguments 

 against it which need not be discussed here. 



Now, why are volcanic rhyolites and other volcanic rocks 

 generally richer in soda than plutonic rocks 1 If assimilation 

 has played an important part in the formation of volcanic 

 magmas, it follows that more soda would be abstracted than 

 potash, inasmuch as soda exists in the sedimentary series as the 

 soluble and volatile chloride, whereas potash exists mainly in the 

 form of insoluble and non-volatile silicates. 



The Evidence of the Crystalline Schists. 



Griibenmann in his excellent work "Die Kristallinen Schiefer" 

 divides these rocks in accordance with mineral composition and 

 textural features into three broad divisions — (1) the kata-rocks 

 which have been formed in the deepest zone where the original 

 characteristics have been completely lost through slow chemical 

 recrystallisations brought about by very high temperature, very 

 strong hydrostatic pressure and weak stress. (2) The meso-rocks 

 which were formed in the middle zone, where temperature was 

 lower, hydrostatic pressure weaker, but stresses very powerful; 

 these forces produced chemical recrystallisations in accordance 

 with Van't Hoff's volume law and Riecke's principle. (3) The 

 e/n-rocks formed in the upper zone at a still lower temperature 

 where hydrostatic pressure was faint or absent, but stresses great, 

 Under these circumstances mechanical deformation was induced in 

 rocks. 



The crystalline schists are distinguished from igneous rocks by 

 their texture, structure, curious mineral composition and their 



