642 



GEOLOGY OP SAMOA AND THE ERUPTIONS IN SAVAII, 



2. General Geology. 



The German Samoan Islands, the chief of which are Upolo, 

 Savaii and Apolima, have been built up from oceanic depths by 

 volcanic action. The same is probably equally true of the other, 

 the American, islands of the group, Tutuila and Manua, which 

 according to the investigations of J. D. Dana* bear a close 

 resemblance to Upolo. 



The islands of Savaii, Apolima, Upolo and Tutuila lie on a line 

 of earth fracture which runs W. 20° N., E. 20° S. (see fig. 1). As 

 Dana points out, the fracture appears to have been widest at the 

 western extremity, where, accordingly^ the largest extravasation 

 of lava has taken place. Through each of the two largest islands, 



Fig.]. 



.Savaii (1,691 sq. kilometers) and Upolo (868 sq kilometers), there 

 runs a mountain range forming a backbone. These ranges consist 

 entirely of basaltic lava and have craters situated on them only 

 a few miles apart so as to appear to be made up of a line of 

 volcanic cones which have fused into a mountain chain. This 

 arrangement points to the probability that the islands have been 



* See ' Geology of The U. S. Exploring Expedition.' 



