X. BOTTOM MATERIAL AND STRATA DETERMINATIONS 

 Adrian F. Richards 



A. INTRODUCTION 



A very good compilation of instruments used more than two decades 

 ago to collect bottom sediments and rock is given by J. L. Hough 

 (Reference X-9). More recently, R. S. Dietz published a brief sum- 

 mary of bottom sampling devices designed between 1940 and 1950 

 (Reference X-3). Operating instructions for a number of bottom 

 samplers have been published by the Hydrographic Office (Reference 

 X-34). In recent years instrumentation has been developed for obtain- 

 ing continuous subbottom reflections of sediment strata. Appendix 

 D of this report contains a comparative tabulation of known continuous- 

 profile devices for which information is available. 



B. BOTTOM SAMPLING EQUIPMENT 



Although sampling gear through the years has become increasingly 

 numerous and varied, bottom samplers fall into three general catego- 

 ries: grab samplers, dredges, and corers. 



1. Grab samplers 



Four types of grab samplers are in use by the Hydrographic 

 Office: the Navy Electronics Laboratory-type clamshell snapper, a 

 clamshell snapper of conventional design, the orange-peel sampler, and 

 the underway bottom sampler or Scoopfish. These samplers are 

 adequate to sample surficial sediments. If a large or somewhat less 

 disturbed sample is required, the Van Veen grab sampler, as modified 

 by the Woods Hole Oceanographic Institution in 1959, can be used. 

 A large- and small- size Van Veen sampler, a Scoopfish, and an orange- 

 peel sampler are considered adequate to handle all grab sampling 

 requirements by the Hydrographic Office. (See References X-4, -14, 

 and -34.) 



2. Dredges 



Three types of dredges are used by the Hydrographic Office: 

 (1) a light-weight, wire mesh, triangular dredge designed for collect- 

 ing biological samples in shallow water, (2) a medium- weight, rigid, 

 steel- sided, rectangular dredge designed for recovering loose rock, 

 and (3) a heavy-weight, chain-link, rectangular dredge designed for 

 breaking off rock in place and for all heavy dredging. These dredges 



X-l 



