1888.] HISTORY OF CHRISTMAS ISLAND. 515 



III. GEOLOGICAL HISTORY. 



The geological history of the island appears to be as follows : — 

 The summit of the submarine volcanic mass has been slowly elevated 

 above the sea to a height of nearly 1200 feet, and as it passed through 

 the zone of lime-forming organisms in shallow water these have in- 

 vested it with a cap of limestone. The upheaval has been arrested 

 at intervals and allowed the formation of reefs which have since been 

 elevated and form the terraces at the sides. At the projecting head- 

 land, where the chief stress of the ocean-currents fell, the reefs have 

 grown less than in the intervals between them ; and since their ele- 

 vation the action of the waves has been greatest at these points ; 

 hence we find that at the headlands the terraced slopes are replaced 

 by a single abrupt descent. At the head of Flying-Fish Cove, how- 

 ever, there is a single high cliff replacing the terraces, though it is 

 protected by a spur sent down on either side, which end in Rocky 

 Point to the east and Smith's Point on the west. This is, perhaps, 

 due to the conformation of the volcanic basis which underlies the 

 limestone. 



Captain Wharton points out {op. cit.) that the raised reefs forming 

 the summit of Christmas Island are the highest that are known in 

 the world. 



I have already said that the island is covered with dense bush. It 

 extends often from the edge of the shore-cliff, where the branches 

 reach out over the sea, to the summit. Hence, it is impossible to 

 obtain any general view over the island, even from the top, and several 

 interesting points as to its inland conformation remain at present 

 undecided. 



There was no sign of standing water or of stream-beds. All the 

 rain that falls, and from the fresh greenness of the vegetation there 

 is evidently an abundant rainfall, soaks at once into the porous 

 limestone-rock and finds its way to the sea below the surface. There 

 is, however, a patch of rounded pebbles near the summit which are 

 described by Mr. Murray as "very much altered volcanic stones, many 

 of them coated on the outside by peroxide of manganese ;" they 

 have no earth about them and cover an ill-defined oval area about 

 38 yards in length, and 10 yards in width, the long axis in the 

 direction of the gentle slope of the surface at this part. It is 

 covered with a bed of tall ferns {Nephrolepis acuta). It occurred to 

 nie that after heavy rains there may be a spring at the upper part 

 of this area, the water reaching the surface here but sinking in again 

 beyond it. 



IV. VEGETATION. 



The shores are fringed with widely-spread littoral plants: — Hibiscus 

 tileaceus, with its beautiful crimson-edged yellow flowers ; Tourne- 

 fortia argentea, a large silvery-green shrub with racemes of closely 

 crowded small white flowers ; while on the shore-cliff grew Scavola 

 koenigii in bright green rhododendron-like masses, with white flowers, 

 the favourite haunt of a brown and white Butterfly, Vadebra macleari. 



