UPPER AND LOWER TERRACES. 77 



northwestern and northeastern points, the former being a rounded knob with 

 steeply inclined flanks rising to 150 feet above the sea level and the latter a 

 sheer vertical cliff 35 feet high to the first terrace. 



The whole island seems to have a northwesterly slope. On both sides of 

 the high kuob just mentioned the cliff is only 6 to 8 feet high to the first ter- 

 race — so low, in fact, that during a calm sea it is entirely practicable to land 

 there in a small row-boat. But from these points eastward the height of the 

 cliff increases to 60 or 70 feet, and on top of this cliff is the lower terrace or 

 flat carrying the gray phosphate, one of the two commercial grades of phos- 

 phate found on the island. This terrace, as the sketch map will plainly 

 show, increases in width as it rises eastward, from a few yards near the west- 

 ern knob to fully 300 yards at the eastern end of the island. 



From this lower terrace the island rises on a 30° slope to about 220 feet 

 above sea level, forming two opposing walls on either side which, coalescing 

 in the western knob, gradually separate eastward to encircle an oblong, oval 

 area, slightly depressed between the walls. This is the upper flat or terrace, 

 containing the red phosphate of the island. 



The greatest elevation on the island is 255 feet above sea-level ; but the 

 average elevation of the upper terrace or flat is not over 230 feet. 



Lulu Bay, the site of the present settlement and shipping wharf, is situ- 

 ated on the southern shore around a small opening in the cliff, 300 feet wide. 

 The name is a misnomer, as there is no bay whatever, the sea beating con- 

 tinuously against a 60-foot cliff, and gradually undercutting it. The depth 

 of water here is at least 10 fathoms, and the absence of good harborage, no 

 less than the difficulties attending the transportation of the material from 

 the diggings to the wharf, have in the past greatly retarded shipments. 



Geology. — The entire island is of recent geological age, and is formed 

 wholly of coralline limestone of several varieties. Superficially this rock, 

 throughout the island, is characterized by a pock-marked, honey-comb 

 structure, with sharp, uneven surfaces. Indeed, everything points to its 

 coralline growth and its subsequent elevation, as opposed to the volcanic 

 origin sometimes suggested. At least a dozen different varieties of coral 

 rock were gathered during my brief stay on the island, besides a number of 

 shells. 



Externally the whole island presents a rough, uneven surface, often diffi' 

 cult and dangerous to walk over after removal of the phosphate. But the 

 underlying rock is compact and close grained, and exhibits a partial strati- 

 fication, well seen in the numerous caves and sink-holes which abound in the 

 different parts of the island. In these caves, whose sides, being less exposed 

 to weathering, present regular surfaces of white and blue limestone, the oc- 

 currence of stalactites hanging from the roof was frequently noticed, although 

 the stalagmitic growth was largely concealed by a deposit of excellent gray 



