374 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



liferous limestone. The character of its magnificent vegetation shows 

 its extent and position, and is in marked contrast to the bare and barren 

 volcanic slopes covered with reddish earth (PI. 197, fig. 2). 



At the base of the volcanic slope forming the eastern side of San 

 Luis d'Apra Harbor is a wide limestone flat varying greatly in width, 

 from a few feet to at least 1000 ; it has been formed by the washing 

 down of hill slope material, which has become mixed with the disin- 

 tegrating coralliferous rock. Upon this flat, and its northern and south- 

 ern extension, cocoanut trees grow in great profusion. 



The road leading to Agana runs north from the landing. It skirts the 

 west shore, crossing successive spurs of elevated limestone rock. At a 

 distance of about two miles we strike the first volcanic ridge ; it extends 

 towards the beach, the road passing round the foot of the volcanic bluff. 

 This ridge is composed of greatly decomposed gray volcanic rock con- 

 taining much hoi'nblende. We next come upon a spur of hard ringing 

 limestone full of corals and of other fossils and of red earth. This and 

 other spurs of coralliferous limestone are all that is left of the former 

 mass of limestone elevated by a volcanic outburst (PI. 194, fig. 3). The 

 slopes of the volcanic hills to the east of the road are covered with red 

 volcanic earth and decomposed volcanic tufa. 



As we go north the limestone spurs increase in height and gradually pass 

 into the limestone mesa of the northern pai't of Guam (PI. 194, figs. 2, 3). 

 From the hill east of Agana (PI. 197, fig. 2) we could see Sta Rosa Peak, 

 a volcanic mass rising from 150 to 200 feet above the general level of the 

 limestone (PI. 198, fig. 3). The surface of the northern part of the island, 

 while generally level (PI. 198, fig. 3), is crossed with crevices and full of 

 pot-holes and sinks and funnel-shaped cavities, the whole pitted and 

 honeycombed and covered with spires and pinnacles — much as we have 

 found the surface of islands composed of old coralliferous limestone in 

 other parts of the Pacific. Northward the island gradually rises to a 

 height of 350 to 500 feet. 



South of Agaiia, at the junction of the volcanic outburst with the 

 elevated coralliferous limestone (PI. 194, fig. 3), we can trace the suc- 

 cessive terraces existing between the shore of Gapan Island and the 



