BY H. I. JENSEN. 517 



the Kiama-Jamberoo series of New South Wales are known with 

 certainty to be Permo-Carboniferous, and alkaline rocks of very- 

 recent age have been erupted from Erebus in Antarctica, and 

 from Kenya and Ruwenzori in Central Africa. However, there 

 seems to be no strong objection to assuming that those processes 

 which made the Eocene a period of alkaline eruptions, set in 

 earlier in some regions than in others, and are still going on locally 

 in some circumscribed regions at the present day. 



A common reason for assigning an old age to some of the 

 alkaline bodies intruded into Palaeozoic strata is the existence of 

 a certain degree of schistosity in the border facies of the rock. 

 The fact is generally ignored that the border facies of alkaline 

 rocks always have a marked tendency to schistosity due to flowage 

 under great pressure. 



Ch. ii. The Possible Mode of Origin of 

 Alkaline, Atlantic or Katepeiric Rocks. 



We see from Ch. i., that most of the world's alkaline rocks of 

 known age were intruded in the Neopyrogenic period, chiefly in 

 the Eocene; and when of this age they occur under closely 

 analogous surroundings. These facts, considered in conjunction 

 with the comparative rarity of alkaline rocks (those of foyaitic 

 magma), suggest that there was a common cause at work all over 

 the earth to produce them. What this cause may have been we 

 will try to enquire into from a theoretical standpoint. 



Although alkaline rocks occur in many parts of the world, they 

 cannot be said to be particularly abundant. We have many 

 intrusives of foyaitic magma in New South Wales, yet the area 

 which they cover is insignificant when compared with the area 

 occupied by rocks of calcic magma. So it is also in other parts 

 of the world. 



We have also seen that the period to which most rocks of the 

 Atlantic type belong was one of great folding, mountain-building, 

 epeirogenic uplifts, subsidences and senkungsfeld-formation, and 

 of intense crumpling of the earth's crust. 



