548 THE DISTRIBUTION, ETC., OP ALKALINE ROCKS, 



We see then that in Africa, a continent exhibiting great homo- 

 geneity, the alkaline rocks are universally connected with the 

 Tertiary faulting and fracturing by which the Indo-African 

 continent was broken up. These rocks are most plentiful in the 

 most fractured regions, as around the Gulf of Aden, the Rift 

 Valley, and the Mozambique Channel. In the highly folded 

 regions of protracted Mesozoic sedimentation they have not been 

 met with, but horizontally bedded Mesozoic rocks of Jurassic age 

 are occasionally found in the areas over which they occur. 



D. North America. 



In this Continent there is a magnificent development of alkaline 

 rocks. 



Before dealing with other localities I wish to draw attention 

 to a paper on the Okanagan Batholith, by R. A. Daley,* which 

 has an important bearing on the origin of alkaline rocks. 



The geological history of the Okanagan Batholith may be 

 summarised as follows : — 



(1) Metamorphosis of Palaeozoic sediments, and the intrusion 

 of a basic complex, and differentiation in Carboniferous times. 



(2) Irruption of a batholith of granodiorite in the Jurassic 

 period. 



(3) Rapid denudation of the granodiorite in the Jurassic, and 

 its covering with Cretaceous sediments in the next period. 



(4) Orogenic disturbances, accompanied by the crushing and 

 shearing of the granodiorite, and the folding of the Cretaceous 

 strata. 



(5) The intrusion of the Kruger alkaline body consisting of 

 nepheline syenite and malignite in Tertiary or very late Creta- 

 ceous (Post-Laramie) times; and 



(6) The Tertiary irruption of a batholith of soda-rich Similka- 

 meen horn-bi-granite or monzonite. 



(7) In later Tertiar}* times the irruption of a batholith younger 

 granite (the Cathedral batholith). 



(8) Olivine basalt intrusions. 



* Bull. Geol. Soc. of America. 



