ON ITS EXTERIOK. VOLCANOES. 



273 



find that the maximum interval is between the third and 

 fourth of the aforesaid five groups, i. e. between the 

 groups of Quito and Peru (fully 960 miles), while the 

 least interval is between the first and second group, those 

 of Mexico and Central America. The four intervals 

 between the five groups are respectively 300, 630, 960, 

 and 540 geographical miles. The great distance be- 

 tween the southernmost volcano of Quito and the 

 northernmost of Peru occasions, at the first moment, 

 the more surprise from the old custom of calling the 

 measurement made on the highlands of Quito "the 

 Peruvian Arc." It is only the smaller and southern 

 portion of the chain of the Andes of Peru that is vol- 

 canic. According to lists which I have prepared after 

 a careful discussion of the most recent data, the follow- 

 ing is a general tabular view of the number of volcanoes 

 in each group. 



According to this estimate, the total number of vol- 

 canoes in the five American groups is ninety-one, of which 

 fifty-six belong to the South American continent. I 

 reckon as volcanoes, in addition to those which are still 

 burning and active, mountains from which eruptions 

 are known to have taken place within historic times, 

 and also mountains which by their structure and by the 



VOL. IV. T 



