BY H. I. JENSEN. 581 



or continent undergoing destruction by trough-faulting. In every 

 case Pakeozoic or Archaean rocks occur not far from the alkaline 

 extrusions, and at no great depth under them. 



As regards the law of succession, we see that the one observed 

 by Richthofen in the Andes, and accepted as general by most 

 geologists, does not hold for alkaline areas. 



In the Dunedin district, as Marshall has shown, the succession 

 is very complex, and a magmatic mixture has taken place in 

 several cases. I have given evidence for a similar mixture of 

 magmas in the Warrumbungles and Nandewars. 



In the Cambewarra-Kiama flows a mixture of magmas has also 

 interfered with the normal succession. But in most cases the 

 succession can be accounted for best by imagining — 



(1) Earth-movements and faulting accompanied by basic intru- 

 sions which may or may not have reached the surface and laccolites 

 in between old sedimentary or metamorphic strata at a great depth. 



(2) Fusion of alkaline Archaean schists and similar rocks of 

 sedimentary origin by the immense friction accompanying earth- 

 movements, and by the heat from basic intrusions, so as to form 

 alkaline magmas. 



(3) Fracturing and expulsion of the alkaline magmas in part. 



(4) Mixing of alkaline magmas with basic ones, and expulsion 

 of mixed products. 



(5) Differentiation of the mixed magmas, and expulsion of 

 differentiation-products. 



Brogger in his second volume of " Die Eruptivgesteine des 

 Kristiania Gebiets" compares the sequence observed at Christiania 

 with that observed in Tyrol. 



I contend that if we imagine stoping and assimilation to have 

 taken place here in a magmatic reservoir at a great depth, and 

 differentiation to have taken place chiefly in the reservoirs now 

 exposed by denudation, almost all the features which have been 

 observed in nature can be explained on the theory outlined above. 



Brogger shows clearly enough that neither in Tyrol nor in the 

 Christiania Gebiet, nor in the Highwood Mountains, Montana, 

 has assimilation of the rocks surrounding the exposed masses- 



