GUAM. 371 



Here and there we could distinguish on the western slope of the volcanic 

 mass the remnant of an ancient elevated coralliferous limestone bluff 

 standing like a wall to indicate the height at which the coralliferous 

 limestone had once existed and the amount of erosion and denudation to 

 which that extremity of the island had been subjected (PI. 194, fig. 3). 



Some of the patches of red earth scattered over the volcanic slopes 

 (PL 197, fig. 2) are probably similar to the red earth so characteristic of 

 many atolls in the Paumotus and of other limestone islands ; it represents the 

 existence of former huge masses of limestone, the iron having accumulated ff 



in sufficient quantities to perceptibly color the slopes on which it has been 

 deposited. Of course, in addition to the iron deposit derived from the 

 limestone, the greater part of the red earth of Guam owes its origin to the 

 disintegration of reddish volcanic ash which has been changed into silt and 

 swejot down the slopes of the hills. 



The harbor of San Luis d'Apra has been formed as an angular sound 

 gradually encroaching into the banks and spits which gave it its original 

 outline. Parts of these banks form the intricate passages between the 

 flats covering the eastern extremity of the harbor and the anchorage (PI. 

 233, fig. 4). To the north, towards the town of Agaiia, a long narrow 

 reef flat stretches at the base of the volcanic slope (PI. 194, fig. 3). This 

 reef flat is covered by the remnants of elevated coralliferous limestone 

 masses ; its eastern outliers are still found on the western volcanic slopes 

 of Guam. 



The southern part of Guam consists of a volcanic massif which has burst 

 through the coralliferous limestone (Pis. 195, fig. 2 ; 197, fig. 1 ; 198, fig. 2) ; 

 at Mount Tinkio it has risen to a height of over 1000 feet. This is the 

 highest point of the volcanic ridge; it has burst through the limestone near 

 AgaSa and extends parallel to the west coast from Agana to the southern 

 point of Guam, running at a distance varying from a mile to two miles from 

 the shore (PI. 238, fig. 4). This ridge slopes rapidly to the west, but towards 

 the east the volcanic slopes pass gradually to the southern part of the east 

 coast of the island (PL 233, fig. 4). Outside of the volcanic slopes run a 

 few limestone outliers, such as Cabras Island (PI. 197, fig. 2), the Orote 

 Peninsula (PL 195, fig. 3), Point Facpi (PL 198, fig. 1), and a line of 



