THE LADRONES. 365 



THE LADRONES. 



Plates m-199; ^82; 233,fign. 4., 5. 



The Ladrones form a line of volcanic islands, many of which are active ; 

 they extend north from Guam as far as the Farallon de Pajaros ; there 

 are no less than twelve active volcanoes in a distance of less than 300 

 miles. The southern groups of the Ladrones are islands partly volcanic 

 and partly composed of elevated coralliferous limestone. In Guam a 

 volcanic massif forms the southern half of the island ; in the northern 

 part Mount Santa Eosa, a volcanic outburst, rises at least 200 feet above 

 the general level of the limestone plateau of Guam. At Rota Island we 

 could only trace the existence of a small volcanic outburst, on the north- 

 western shore of the island. 



The islands of the next cluster to the north, Saipan, Tinian, and Aguijan, 

 are partly volcanic and partly limestone ; we did not visit them, but their 

 probable geological structure is indicated by the sketches given on the 

 Hydrographic Charts.^ 



The line of the Lndrones beginning at Santa Rosa reef forms a gigantic 

 flat arc ; the southern portion rims from the southwest to the northeast, 

 the central portion runs nearly due north, and the northern group extends 

 in a somewhat northwesterly direction. Between the Ladrones and Japan 

 a line of volcanic islands extends somewhat to the west of the line of the 

 Ladrones ; its principal groups are the Volcano, the Bonin Islands, Lot's 

 Wife, Aoga-sima, and the volcanic islands and islets which run south of 

 Oosima. These form a line of active volcanoes running for more than 20' 

 of latitude, from the southern part of the Ladrones to the south coast of 

 Japan. The line of soundings of the " Nero " ^ indicates the remarkably 

 uneven character of the bottom along that line of volcanic islands. 



The irregularity of the bottom along that line is in marked contrast to 

 the line of soundings at right angles to it, extending from Guam to Midway 

 Island ; the latter indicates a fairly uniform level bottom of an average 



1 H. O. Chart 1748. 2 h. O. Chart 529. 



