xxvi MAGNETIC ROCKS 371 



It is, however, noteworthy, as indicated by the value of the 

 average in each series that not one of them is a good series. They 

 form curves which in each case present an extreme maximum 

 variant which is suggestive of quite another degree of magnetising 

 agency. This is also illustrated in the combined curve of all the 

 results given above. The acid as well as the basic series are thus 

 characterised, and the extreme maximum variants are in each 

 instance afforded by the highest mountain peaks. It is probable 

 that there is an accelerating ratio of magnetisation with increased 

 elevation. However that may be, it appears evident from my obser- 

 vations on the two adjacent peaks of Ngaingai and Navuningumu 

 that the limits of polarity acquired through atmospheric electricity 

 without the direct action of lightning would be, as measured by 

 the scale here employed, four times as great for a dacite (25) as 

 for a basaltic andesite (90). 



B B 2 



