40O 



PRINCIPLES OF STRATIGRAPHY 



to a depth of about three or four fathoms, is bounded by a sub- 

 marine clifif. This in one section (No. i) continues ahiiost un- 

 broken to a depth of about 500 feet, except that a kind of edge or 

 terrace is clearly indicated at a depth of rather less than 100 feet. 

 In the other section the foot of the great submarine cliff is 

 found at about 500 feet, but . . . the cliff is distinctly divided into 

 two precipices by a shelving bank of coral and sand, which begins at 

 a depth of about 140 feet and reaches the brow of the lower preci- 

 pice at about 260 feet. This bank is covered by 'sand and coral.' At 



No. I. 



Fig. 79. Section i of Masamarhu Island in the Red Sea, showing the char- 

 acters of the slopes according to Captain Maclear. (After Savillc- 

 Kent.) 



this depth in each section the island is, as it were, defended by a 

 deep and narrow ditch, the edge of its steep glacis being formed by 

 a sharp arete of coral which in one case rises into soundings of 

 about 250 feet." (Bonney-13.) From this the first section rapidly 

 falls to a second ditch, the bottom of which is more than 1,200 feet 

 below sea-level, while its counterscarp rises more than 300 feet. 

 Beyond this, after a level stretch, the slope descends at about 30 

 degrees. The second ditch is wanting in the second section. Coral 

 and sand are found in the bottom of the ditches, and the two 

 aretes are formed by coral apparently grown in situ. This would 



