The remainder probably will require explanatory help from the teacher 

 or parents. Authoritative references containing additional details on each 

 question are given; many of these books may be found in school libraries 

 or can be easily obtained by instructors or students. 



To our readers, we hope the information herein will promote further 

 exploration into the wealth of material available on the oceans. We 

 sincerely hope it will serve as a threshold to students seeking interesting 

 challenges for study. To those who seek careers in virgin frontiers, we 

 suggest serious consideration of the opportunities for investigation, re- 

 search, and discovery in the marine sciences. If additional assistance or 

 information is desired, we invite you to write us at the National Oceano- 

 graphic Data Center. 



