366 "ALBATROSS" TKOTICAL PACIFIC EXPEDITION. 



depth of about 2700 fathoms. Across the south of Guam extend "Caroline 

 and Nero Deeps " ; tliej' are probably the eastern extension of " Challenger 

 Deep." Thi.s deep valley, with a greatest depth of 52G9 fathoms, sepa- 

 rates the Ladrones from the Carolines. 



Guam. 



Plates J9>f-19.S ; 233; 233, fig. 4, 



The island of Guam is rectangular, about twenty-two miles in length ; 

 its greatest width across the southern part is eight miles, and in the 

 northern sis miles, narrowing near the central part of the island at the 

 latitude of Tumun Bay to about three miles in width (PI. 233, fig. 4). 

 South of the central part of the western shore, between Agaiia and Agate 

 Bay, extends the peninsula of Orote ; it runs out four miles in a noi-th- 

 westerly direction, and forms the southern side of the haibor of San Luis 

 d'Apra ; the north side is protected by Cabras Island, about two miles in 

 length ; its western extension has been denuded and eroded into a wide 

 barrier reef flat, Luminan Reef and Calalan Bank extending as far as 

 Spanish Rock, the western extremity of the northern strip enclosing the 

 Bay of San Luis d'Apra (PI. 195, fig. 1). This bay has been eroded out 

 of the elevated coralliferous limestone of which the northern part of 

 the island of Guam consists. 



From Port Pago north (PI. 233, fig. 4), on the east coast, are most 

 distinct coralliferous limestone terraces, marking the position of the former 

 sea level, and indicating the periods of rest during the elevation of 

 Guam ; where they are not well defined their position is still indicated 

 by the lines of caverns which crop out in the vertical faces, and give an 

 indication of the position of former lines of sea level. The mode of 

 formation of the vertical cliffs of the eastern side of the island, by the 

 gradual sloughing off of the lower parts of the vertical faces and encroach- 

 ing upon successive terraces, is well seen north of Anao Point ; the parts 

 thus falling off remain as outliers of the older terraces on the narrow 

 shore platform. The vertical cliffs of the northern part of Guam vary in 



