RECENT ADVANCES IN SCIENCE 33 



taceous and the Tertiary in Patagonia. This hiatus is corre- 

 lated with the first phase of the Andean orogenic movements. 

 On the epeirogenic side these movements caused the fragmenta- 

 tion of the Brazilo-Ethiopian continent, and the formation of 

 the South Atlantic basin ; which, in turn, opened the way for 

 the Tertiary transgression over the Patagonian continent. 



Petrology. — In his Presidential Address to the Geological 

 Society, Dr. A. Harker considers the relation between igneous 

 action and crustal movements in Britain (Proc. Geol. Soc. 191 8, 

 73, pt. 1, lxvii-xcvi). The distribution of the alkalic and calcic 

 provinces in relation to the great Lewisian, Caledonian, and 

 Hercynian orogenic movements, and to the formation of the 

 North Atlantic basin in Tertiary times, is traced ; and it is 

 shown how closely alkalic and calcic facies follow crustal 

 movements which are, respectively, of dominantly vertical or 

 horizontal character. 



In a review of recent work, especially Bowen's, on pedo- 

 genesis, Prof. R. A. Daly is led to renewed faith in the general 

 explanation advanced by him for the origin of the alkaline 

 rocks (Journ. Geol. 1918, 26, 97-134). His well-known hypo- 

 thesis is that of control by the syntexis of basic sediments 

 charged with volatile matter ; and he believes that it explains 

 all the characteristic features of the alkaline rocks, while not 

 open to certain special difficulties which beset Bowen's theory 

 of pure fractional differentiation. 



Prof. A. Johannsen has made an elaborate scheme for the 

 quantitative mineral classification of igneous rocks (Journ. 

 Geol. 1917, 25, 63-97). The graphic basis of his method is a 

 double tetrahedron, each of the five trihedral angles of which 

 represent certain mineral constituents: (1) quartz; (2) potash 

 felspar with the Or. molecule in anorthoclase, (3) plagioclase 

 with the Ab. molecule in anorthoclase; (4) felspathoids ; 

 (5) mafic minerals. Any rock of which the mineral com- 

 position is quantitatively known may thus be referred to a 

 point within this figure. The method of further subdivision 

 is too complicated to indicate in a short paragraph, but it 

 provides a quantitative basis for, and utilises, the existing 

 nomenclature, with the minimum amount of disturbance and 

 renaming. 



Prof. S. J. Shand has also presented a new classification of 

 igneous rocks based primarily on his notion of the degree of 

 3 



