part 1] 



PHOSPHATE DEPOSIT OP OCEAN ISLAND. 



9 



north-east and west- south- west, and its position is indicated on the 

 accompanying plan (fig. 2). The plane rises north-north-west- 

 wards at an angle of 0° 17', and plunges below the sea south-south- 

 eastwards at the same angle. 



(6) Analyses of samples taken in excavations show that the 

 percentage of tricalcium phosphate in the deposit increases steadily 

 with height above this datum-plane until a maximum of 92 per 

 cent, is reached, at a point which, though not the highest point of 

 the island, is the one farthest from the datum-plane. The change 

 in the phosphatic content of the deposit as -one approaches or 



Fig. 2. — Sketch-map of Ocean Island. 



«*»■ 



r [Phosphate 



i Nautical Mile 



recedes from the datum-plane is quite regular ; in fact, it may be 

 stated that the percentage of tricalcium phosphate at any point of 

 the deposit is a straight-line function of the distance of that point 

 from the datum-plane. 



(7) Below the datum-plane the phosphate content falls at the 

 same rate as above, to about 79 per cent. Lower than this, no 

 phosphate deposits of any extent have been found, either the coast 

 being reached or the deposit petering out and being replaced by 

 unphosphatized coral-rock or coral-debris. 



(8) The existence of this law of distribution makes it possible 

 to predict with considerable accuracy the quality of phosphate to 

 be expected in new areas of the island, to form an approximate 



