8 DEVELOPMENT OF PETROLOGY. 



On the question of Alkaline Rocks to which gradually 

 increasing importance has been attached, Daly furnished 

 during 1910 an interesting hypothesis with regard to their 

 origin. His hypothesis is that most of the alkaline species 

 are formed by the interaction of basaltic magma and lime- 

 stone. 



This view as to the origin of alkaline rocks is still 

 in the hypothetical stage, and as far as Australian repre- 

 sentatives of these rocks are concerned, it has not been 

 very favourably received. 



In the succeeding year, 1911. Daly in '" Magmatic 

 Differentiation in HaAvaii." stated as his belief that " all late 

 pre-C'ambrian and younger " Alkaline " rocks are the result 

 of differentiation \^ithin primary basaltic magma or within 

 syntectic magmas formed by the solution of solid, generally 

 sedimentary, rock in the primary basalt. The marvellously 

 uniform composition of the basaltic magma issuing from 

 countless fissures in every ocean basin, as in every conti- 

 nental plateau, seems capable of explanation only on the 

 premise that it forms the material of a continuous world- 

 circling substratum. The facts of geology suggest that 

 this substratum was formed by an ancient liquidation 

 which took place when the globe was molten at the surface." 

 He also holds that the division of igneous rocks into 

 '■ Atlantic '" and " Pacific " groups as suggested by Becke 

 and so strongly advocated by Harker, is not warranted. 

 On this latter question Cross, Iddings, and others are with 

 Daly. 



In the ■' Origin of Igneous Rocks " (1911) by F^ 

 Loewinson-Lessing we find a modification of the ideas 

 which were held by Bunsen and Michel Levy. 



The author concludes that there are two original 

 independent magmas and that these predominate in the 

 earth's crust. These two primordial magmas are the 

 granitic and gabbroidal (basaltic) and all other igneous 

 rocks are derivations from them and subordinate to 

 them in their occurrence. All igneous rocks belong to 

 those types : (1) primordial jnagmas : (2) rocks due to 

 differentiation ; (3) rocks j^roduced by a mingling of the 

 two magmas. In addition, all igneous rocks of all geo- 

 logical periods originated principally by the refusion of 



