8 BASIC AND ULTRABASIC IGNEOUS ROCKS— BENSON. [Mmwe ?& a "six; 



be looked for, "inasmuch as there is a certain tendency for successive systems of crust-move- 

 ments, even at wide intervals of time, to follow in some measure the same general lines. " (Harker 

 '09, p. 105.) In the contrast between the conditions of the Tertiary alkaline rocks of the Bohe- 

 mian Mittlegebirge, almost undisturbed save for block-faulting, with the roughly coeval green- 

 rocks of the Apennines, which have suffered intense dislocation, we see that the difference in their 

 history subsequent to their eruption accords with the difference in the tectonic conditions, 

 plateau as against geosyncline, of their place of development, and may notice a corresponding 

 difference in the original petrographical character of the rocks themselves. 



