BY HENRY C. RICHARDS, M.SC. 1 1 



chemical differences of the magmatic series ; nor does it 

 appear that the generaUzation of distribution appUes to 

 the older roclts. 



Several other authors have expressed their views on 

 the origin of Alkaline Rocks. Becke suggested that during 

 a gaseous stage of the earth the action of gravity separated 

 the magma into an upper, subalkaline or calcic, layer and 

 a lower, alkaline, layer. 



Jensen suggested " that alkaline rocks are derived 

 from Archiean saline beds, which by chemical attacks on 

 the adjacent sediments, have given rise to an alkaline magma 

 in the process of metamorphosis. This magma has been 

 squeezed laterally into continental areas and has undergone 

 differentiation, or it has mixed with other magmas, chiefly 

 basic, and then differentiated. 



The views of Marker and Dali/ have already been given. 

 C.H. Smyth, Junr. however, suggests that alkaline rocks 

 are derived from ordinary subalkaline magmas through the 

 agency of inineralisers. 



The present position with respect to Metamorphic rocks 

 is that two of the fundamental problems of the origin of 

 crystalline schists are now settled, viz., the source of the 

 crystalhne rocks and their relation to time. It is generally 

 accepted that they have been developed from both igneous 

 and sedimentary rocks in various periods and not in 

 Archaean times alone as previously supposed. There are 

 two divergent views, however, as to the mode of origin ; 

 (1) that the processes of development are devoid of the 

 agency of igneous rocks ; (2) that the agency of igneous rocks 

 is the controlhng factor. 



