31 6 . REGINALD A. DALY 



theralitic, or other alkaline habit are already known, and the 

 number of occurrences in that part of the earth is constantly- 

 growing. It may be quite true that alkaline rocks are more 

 abundant on the Atlantic side of the globe — possibly because thick 

 prisms of calcareous sediments are, in proportion to area, more 

 developed in the Atlantic region— but it is yet more apparent that 

 the overwhelming mass of the igneous rocks in the Atlantic region 

 are subalkaline in type. The distinction of the two "Atlantic and 

 Pacific races" (Sippen) is not only fallacious in the literal, geo- 

 graphic sense ; it introduces an unnecessary pair of terms of quite 

 elusive definition in place of the well-established, less nebulous 

 terms "alkaline" and "subalkaline." The proved difficulty of 

 making a clean-cut definition of the expression "alkaline rock" finds 

 explanation in the theory that all late pre-Cambrian and younger 

 alkaline rocks are of secondary origin, because derived from basalt 

 or from its syntectics. According to this view, many transi- 

 tional types should be found between the highly alkaline species 

 and those low in alkalies; iron-clad definition becomes impossible. 



