comparison of the sounding surveys indicated erosion or accretion. Instal- 

 lation by scuba divers would include a reference mark or measurement to 

 record the bottom elevations at each reference mark. Subsequent checks 

 would give a relatively precise measurement of elevation changes, thereby 

 providing reliable data concerning the pattern and rates of erosion and 

 accretion of bottom sediments in the vicinity of the island. 



57 



