TRUE VOLCANOES. 269 



lation gives 2540 against 2428 geographical miles) is occu- 

 pied by volcanoes. If we examine the distribution of the 

 space free from volcanoes between the five volcanic groups, 

 we find the maximum distance of two groups from one an- 

 il. Distance of the Mexican group from the next group, that of Cen- 

 tral America (from the volcano of Orizaba to the volcano of So- 

 conusco, in the direction E.S.E. — W.N.W.), 300 miles. 



III. Group of the Volcanoes of Central America : Its length from S.E. 

 to N.W., from the volcano of Soconusco to Turrialva, in Costa 

 Eica, more than 680 miles. 



IV. Distance of the group of Central America from the series of 

 volcanoes of New Granada and Quito, 628 miles. 



V. Group of the Volcanoes of New Granada and Quito : Its length from 

 the eruption in the Paramo de Ruiz to the north of the Volcan de 

 Tolima, to the volcano of Sangay, 472 miles. The portion of the 

 chain of the Andes between the volcano of Purace, near Popayan, 

 and the southern part of the volcanic mountain group of Pasto is 

 directed N.N.E. — S.S. W. Far to the eastward from the volcanoes 

 of Popayan, at the sources of the Rio Fragua, there is a very iso- 

 lated volcano, which I have inserted upon my general map of the 

 mountain group of the South American Cordilleras, from the 

 statements of missionaries from Timana, which were communi- 

 cated to me : distance from the sea-shore, 152 miles. 



VI. Distance of the volcanic group of New Granada and Quito from 

 the group of Peru and Bolivia, 960 miles, the greatest length des- 

 titute of volcanoes. 



Vil. Group of the Series of Volcanoes of Peru and Bolivia, from the 

 Volcan de Chacani and Arequipa to the volcano of Atacama (161:° 

 — 21J°), 420 miles. 



VIII. Distance of the Group of Peru and Bolivia from the volcanic 

 group of Chili, 540 geographical miles. From the portion of the 

 desert of Atacama, on the border of which the volcano of San 

 Pedro rises, to far beyond Copiapo, even to the volcano of Co- 

 quimbo (30° 5'), in the long Cordillera to the west of the two prov- 

 inces Catamarca and Rioja, there is no volcanic cone. 



IX. Group of Chili, from the volcano of Coquimbo to the volcano 

 San Clemente, 968 miles. 



These estimates of the length of the Cordilleras, with the curvature 

 which results from the change in the direction of the axis, from .the 

 parallel of the Mexican volcanoes in ]9i° N. lat., to the volcano of 

 San Clemente in Chili (46° 8' S. lat.), give, for a distance of 4968 

 miles, a space of 2540 miles which is covered by five linear groups of 

 volcanoes (Mexico, Central America, New Granada with Quito, Peru 

 with Bolivia, and Chili); and a space probably quite free from volca- 

 noes of 2428 miles. The two spaces are nearly equal. I have ffiven 

 very definite numerical relations, as obtained by the careful criticism 

 of my own maps and those of others, in order to give rise to a greater 

 desire to improve them. The longest portion of the Cordilleras free 

 from volcanoes is that between the groups of New Granada with Quito, 

 and Peru with Bolivia. It is accidentally equal to that occupied by 

 the volcanoes of Chili. 



